A 12-Month Randomized Clinical Trial of 38% SDF vs. Restorative Treatment.

PURPOSE: The aim of this 2-arm, parallel-group, 12-mo randomized clinical trial was to compare the effectiveness of semiannual application of 38% silver diamine fluoride (SDF) versus restorative treatment (RT) to manage cavitated caries lesions in primary teeth in a diverse population of children in Michigan. METHODS: Children aged 2 to 10 y with at least 1 soft cavitated lesion (International Caries Detection and Assessment System 5 or 6) with no pain or signs/symptoms of irreversible pulpitis were recruited and randomly assigned to 2 intervention groups. One random lesion per child received 38% SDF (twice, at a 6-mo interval) or RT. All interventions and assessments were done by calibrated dentists. Primary outcome measures were clinical failure rates: minor (e.g., reversible pulpitis, active/soft lesion or progression, restoration loss or need for replacement/repair, secondary caries) and major (e.g., irreversible pulpitis, abscess, extraction). Parent, child, and provider acceptability was also assessed. RESULTS: Ninety-eight children were enrolled and randomized, with a mean (SD) age of 4.8 y (1.8); 46% were female and their mean dmft + DMFT was 6.3 (3.9). Sixty-nine children were assessed at 12 mo (sample was within the planned 30% attrition rate). There were significantly more teeth with minor failures (SDF = 65%, RT = 23%, P ≤ 0.001) and major failures (SDF = 13%, RT = 3%, P ≤ 0.001) in the SDF group than the RT group; 74% of SDF-treated lesions were hard at 12 mo vs. 57% at 6 mo. Providers stated that SDF was easier, faster, and more preferable than RT (P ≤ 0.001). No significant differences were found in parental satisfaction and acceptability. At 12 mo, children in the RT arm felt significantly (P < 0.05) happier with their tooth appearance and stated that their visit to the dentist hurt less. CONCLUSION: At 12 mo, SDF-treated lesions had significantly more minor and major failures than RT, suggesting that SDF-treated teeth need to be closely monitored in a population at high caries risk (ClinicalTrials.gov NCT02601833). KNOWLEDGE OF TRANSFER STATEMENT: The results of this study can be used by clinicians when deciding whether to restore or apply silver diamine fluoride to cavitated lesions in primary teeth. Information on treatment outcomes and parent, child, and provider acceptability can help guide appropriate treatment decisions and need for monitoring.

WITHDRAWN: Selective serotonin reuptake inhibitors (SSRIs) versus other antidepressants for depression.

BACKGROUND: The relatively new class of antidepressant, the selective serotonin reputake inhibitors (SSRIs), may be better tolerated than the older tricyclic antidepressants. This review compares the efficacy of SSRIs with other antidepressants. OBJECTIVES: To examine the relative efficacy of selective serotonin reuptake inhibitors (SSRIs) compared to other antidepressants. SEARCH STRATEGY: The search strategy included a search of (a) Electronic bibliographic databases (MEDLINE, EMBASE); (b) reference lists of related reviews (c) reference lists of all located studies (d) contact with the manufacturer and (e) the Cochrane Group register of controlled trials SELECTION CRITERIA: Randomised controlled trials comparing selective serotonin reuptake inhibitors with other kinds of antidepressants in the treatment of patients with depressive disorders. The outcome measures assessed included measures of the severity of depression. DATA COLLECTION AND ANALYSIS: Data were collected from each study the main outcome measurefrom each study. These included: mean Hamilton depression rating scale, mean Montgomery & Asberg depression rating scale, Clinical Global Impression rating scale. An analysis of standardised mean difference of these scales was performed using Review Manager 3.1 software. The presence of heterogeneity of treatment effect was assessed MAIN RESULTS: Ninety-eight trials contributed data to the analysis of the relative efficacy of SSRIs and related drugs with comparator antidepressants (Figure 3 & Appendix 3). Analysis of efficacy was based upon 5044 patients treated with an SSRI or related drug, and 4510 treated with an alternative antidepressant. The standardised effect size for SSRIs and related drugs together versus alternative antidepressants using a fixed effects model was 0.035 (95% CI -0.006 to 0.076; Q = 149.25, df = 97, p < 0.001). AUTHORS' CONCLUSIONS: There are no clinically significant differences in effectiveness between selective serotonin reuptake inhibitors and tricyclic antidepressants. Treatment decisions need to be based on considerations of relative patient acceptability, toxicity and cost.

WITHDRAWN: Treatment discontinuation with selective serotonin reuptake inhibitors (SSRIs) versus tricyclic antidepressants (TCAs).

BACKGROUND: Selective serotonin reuptake inhibitors are thought to have better discontinuation rates (i.e. less people dropping out) than tricyclic and heterocyclic antidepressant drugs. It is important to quantify the drop-out rates of different antidepressant drugs in order to have a better understanding of the relative tolerability of these drugs. OBJECTIVES: To assess the comparative tolerability of selective serotonin reuptake inhibitors and tricyclic/heterocyclic antidepressant drugs. SEARCH STRATEGY: We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Registers (1997 to 1999), MEDLINE (1966 to 1999), EMBASE (1974 to 1999) We also searched specialist journals, the reference lists of relevant papers and previous systematic reviews, conference abstracts and government documents. Representatives of the pharmaceutical industry were contacted. SELECTION CRITERIA: Parallel group randomised controlled trials comparing selective serotonin reuptake inhibitors with tricyclic or heterocyclic antidepressants in people with depression. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and a third reviewer checked any cases of disagreement. MAIN RESULTS: We included 136 trials. The selective serotonin reuptake inhibitors showed less participants dropping out compared to the tricyclic/heterocyclic group (odds ratio 1.21, 95% confidence interval 1.12 to 1.30). A statistically significant difference was found in total drop-outs between the selective serotonin reuptake inhibitors and the old tricyclics as well as the newer tricyclics. When the selective serotonin reuptake inhibitors were compared to the heterocyclic antidepressants, there was a non significant difference favouring the selective serotonin reuptake inhibitors. The poor tolerability profile of the old tricyclics was explained by differences in drop-outs for side-effects, but not for inefficacy. AUTHORS' CONCLUSIONS: Whilst selective serotonin reuptake inhibitors do appear to show an advantage over tricyclic drugs in terms of total drop-outs, this advantage is relatively modest. This has implications for pharmaco-economic models, some of which may have overestimated the difference of drop-out rates between selective serotonin reuptake inhibitors and tricyclic antidepressants. These results are based on short-term randomised controlled trials, and may not generalise into clinical practice.

The effect of forearm bracing on radioulnar impingement.

The purpose of this clinical study was to compare patients' symptoms and radioulnar convergence following distal radioulnar reconstruction with and without a functional brace on. Standardized radiographs were taken of the involved wrist at rest, while holding a weight, and during maximum power grip. All radiographs were then repeated while wearing a prefabricated functional brace (Maramed, Miami, FL). The functional brace did not decrease radioulnar convergence and, at rest, the brace actually increased radioulnar convergence. Despite this, all patients who experienced pain without the brace were pain free with the brace on. We conclude that forearm bracing may be a useful nonoperative treatment for residual pain following DRUJ salvage surgery, though its mechanism of action is unclear.

Indicators of fatigue and of prolonged weaning from mechanical ventilation in surgical patients.

Indicators of weaning success have been tested primarily in patients who have been ventilated for short periods of time, and they may not be as accurate in cases where support has been required for longer than a few days. In patients requiring longer periods of support it is difficult to estimate the likelihood of successful liberation. Therefore we evaluated established weaning indices for their accuracy in surgical patients who required > or = 72 hours of mechanical ventilation. Surgical patients who required mechanical ventilation for > or = 72 hours were prospectively followed (over 6 months). We obtained standard indices of ventilatory function daily once patients were ready to wean. These indices included the respiratory rate/tidal volume ratio (RSBI), the maximal inspiratory pressure, and the minute ventilation. The duration of weaning and explicitly defined episodes of fatigue were the outcomes of interest. Statistical analyses evaluated the multiple factors that might influence the duration of weaning. Ninety-five patients (66% trauma; 34% surgery) survived to begin weaning, and 93% were liberated. The median duration of mechanical ventilation prior to weaning was 4 days (range 3-16 days), and the median duration of weaning was 3 days (range 0-56 days). Fatigue occurred in 36 patients and was not reliably predicted by any of the weaning measurements. However, a RSBI of > 105 on the first day of weaning was associated with prolonged weaning. By multivariate analysis, an RSBI of > 105 on the first day of weaning predicted prolonged weaning (hazard ratio 1.9; p = 0.03). After 72 hours of mechanical ventilation, clinical fatigue and successful liberation are not reliably predicted by standard indices of respiratory muscle strength and reserve. However, an RSBI of >105 observed once the patient is ready to wean is associated with prolonged weaning.

Chloroplast ribosomal protein S7 of Chlamydomonas binds to chloroplast mRNA leader sequences and may be involved in translation initiation.

Certain mutations isolated in the 5' untranslated region (5'UTR) of the chloroplast rps7 gene in Chlamydomonas reduce expression of reporter genes. Second site suppressors in this 5'UTR sequence restore reporter expression. 5'UTR sequences with the original mutations fail to bind a 20-kD protein, one of five proteins that bind to leaders of several chloroplast genes. However, 5'UTRs from suppressed mutants restore binding to this protein but do not bind a 47-kD protein present on the wild type and the original mutant 5'UTRs. The 20-kD protein was shown to be the S7 protein of the chloroplast ribosomal small subunit encoded by rps7, whereas the 47-kD protein was shown to be RB47, a poly(A) binding protein. Our data are consistent with the hypothesis that the S7 protein plays either a general or a specific regulatory role in translation initiation in the chloroplast.

Very high light resistant mutants of Chlamydomonas reinhardtii: Responses of Photosystem II, nonphotochemical quenching and xanthophyll pigments to light and CO(2).

We have isolated very high light resistant nuclear mutants (VHL (R)) in Chlamydomonas reinhardtii, that grow in 1500-2000 mumol photons m(-2) s(-1) (VHL) lethal to wildtype. Four nonallelic mutants have been characterized in terms of Photosystem II (PS II) function, nonphotochemical quenching (NPQ) and xanthophyll pigments in relation to acclimation and survival under light stress. In one class of VHL (R) mutants isolated from wild type (S4 and S9), VHL resistance was accompanied by slower PS II electron transfer, reduced connectivity between PS II centers and decreased PS II efficiency. These lesions in PS II function were already present in the herbicide resistant D1 mutant A251L (L (*)) from which another class of VHL (R) mutants (L4 and L30) were isolated, confirming that optimal PS II function was not critical for survival in very high light. Survival of all four VHL (R) mutants was independent of CO(2) availability, whereas photoprotective processes were not. The de-epoxidation state (DPS) of the xanthophyll cycle pigments in high light (HL, 600 mumol photons m(-2) s(-1)) was strongly depressed when all genotypes were grown in 5% CO(2). In S4 and S9 grown in air under HL and VHL, high DPS was well correlated with high NPQ. However when the same genotypes were grown in 5% CO(2), high DPS did not result in high NPQ, probably because high photosynthetic rates decreased thylakoid DeltapH. Although high NPQ lowered the reduction state of PS II in air compared to 5% CO(2) at HL in wildtype, S4 and S9, this did not occur during growth of S4 and S9 in VHL. L (*) and VHL (R) mutants L4 and L30, also showed high DPS with low NPQ when grown air or 5% CO(2), possibly because they were unable to maintain sufficiently high DeltapH due to constitutively impaired PS II electron transport. Although dissipation of excess photon energy through NPQ may contribute to VHL resistance, there is little evidence that the different genes conferring the VHL (R) phenotype affect this form of photoprotection. Rather, the decline of chlorophyll per biomass in all VHL (R) mutants grown under VHL suggests these genes may be involved in regulating antenna components and photosystem stoichiometries.

[Elective surgery--cancellations, ring fencing and efficiency]. / Elektiv kirurgi--strykninger, skjerming og effektivitet.

BACKGROUND: We set out to study to what extent emergency admissions disturb elective surgical activities, resulting in decreasing efficiency and fewer elective procedures. We looked at the evidence of whether ring fencing elective surgery is an effective strategy to reduce disturbance from emergency activities, and improve the overall efficiency in hospitals with emergency as well as elective activities. MATERIAL AND METHODS: We systematically searched for published studies that have addressed the above mentioned issues. RESULTS: Approximately 10-17% of elective surgical operations are cancelled. In a Norwegian study, about 14% of cancellations seem to be caused by interference from emergency admissions. We did not find any empirical evidence on the effects of ring fencing elective surgery. INTERPRETATION: The belief that ring fencing is an effective strategy to decrease cancellations and increase hospital efficiency seems to be anchored in a priori reasoning rather than in published evidence.

Mutations that alter the higher-order structure of its 5' untranslated region affect the stability of chloroplast rps7 mRNA.

In this paper, we examine the effects of mutations in the 5'UTR of the chloroplast rps7 transcript of Chlamydomonas reinhardtii that reduce the stability of the mRNA. Five point mutants in the rps7 5'UTR were selected on the basis of their failure to accumulate reporter mRNA in Escherichia coli. Each of these mutations produces alterations in the predicted higher-order structures of the rps7 5'UTR that destabilize the mRNA. Cis-acting suppressors of these mutations have been selected in E. coli and in the C. reinhardtii chloroplast that restore message stability and function. No differences in RNA melting and reannealing profiles have been observed between wild type, original mutant, and suppressor 5'UTRs transcribed in vitro. Proteins of 32 kDa and 47 kDa that bind to the wild-type rps7 5'UTR are not detected by UV cross-linking assays performed with any of the mutant rps7 5'UTRs. However, binding of the 32-kDa protein is restored in the six suppressor mutants examined. This suggests that the 32-kDa protein may be involved in protecting the rps7 5'UTR and the attached coding region from digestion by ribonucleases. Alternatively, the binding site for the 32-kDa protein may be independently lost in the rearranged tertiary structure of the mutant 5'UTR that exposes the RNA to degradation and is restored in the suppressor mutants.

Selective serotonin reuptake inhibitors versus tricyclic and heterocyclic antidepressants: comparison of drug adherence.

BACKGROUND: Selective serotonin reuptake inhibitors are thought to have better discontinuation rates (i.e. less people dropping out) than tricyclic and heterocyclic antidepressant drugs. It is important to quantify the drop-out rates of different antidepressant drugs in order to have a better understanding of the relative tolerability of these drugs. OBJECTIVES: To assess the comparative tolerability of selective serotonin reuptake inhibitors and tricyclic/heterocyclic antidepressant drugs. SEARCH STRATEGY: We searched the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Registers (1997 to 1999), MEDLINE (1966 to 1999), EMBASE (1974 to 1999) We also searched specialist journals, the reference lists of relevant papers and previous systematic reviews, conference abstracts and government documents. Representatives of the pharmaceutical industry were contacted. SELECTION CRITERIA: Parallel group randomised controlled trials comparing selective serotonin reuptake inhibitors with tricyclic or heterocyclic antidepressants in people with depression. DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and a third reviewer checked any cases of disagreement. MAIN RESULTS: We included 136 trials. The selective serotonin reuptake inhibitors showed less participants dropping out compared to the tricyclic/heterocyclic group (odds ratio 1.21, 95% confidence interval 1.12 to 1.30). A statistically significant difference was found in total drop-outs between the selective serotonin reuptake inhibitors and the old tricyclics as well as the newer tricyclics. When the selective serotonin reuptake inhibitors were compared to the heterocyclic antidepressants, there was a non significant difference favouring the selective serotonin reuptake inhibitors. The poor tolerability profile of the old tricyclics was explained by differences in drop-outs for side-effects, but not for inefficacy. REVIEWER'S CONCLUSIONS: Whilst selective serotonin reuptake inhibitors do appear to show an advantage over tricyclic drugs in terms of total drop-outs, this advantage is relatively modest. This has implications for pharmaco-economic models, some of which may have overestimated the difference of drop-out rates between selective serotonin reuptake inhibitors and tricyclic antdepressants. These results are based on short-term randomised controlled trials, and may not generalise into clinical practice.

SSRIs versus other antidepressants for depressive disorder.

OBJECTIVES: To examine the relative efficacy of selective serotonin reuptake inhibitors (SSRIs) compared to other antidepressants. SEARCH STRATEGY: The search strategy included a search of (a) Electronic bibliographic databases (MEDLINE, EMBASE); (b) reference lists of related reviews (c) reference lists of all located studies (d) contact with the manufacturer and (e) the Cochrane Group register of controlled trials SELECTION CRITERIA: Randomised controlled trials comparing selective serotonin reuptake inhibitors with other kinds of antidepressants in the treatment of patients with depressive disorders. The outcome measures assessed included measures of the severity of depression. DATA COLLECTION AND ANALYSIS: Data were collected from each study the main outcome measurefrom each study. These included: mean Hamilton depression rating scale, mean Montgomery & Asberg depression rating scale, Clinical Global Impression rating scale. An analysis of standardised mean difference of these scales was performed using Review Manager 3. 1 software. The presence of heterogeneity of treatment effect was assessed MAIN RESULTS: Ninety-eight trials contributed data to the analysis of the relative efficacy of SSRIs and related drugs with comparator antidepressants (Figure 3 & Appendix 3). Analysis of efficacy was based upon 5044 patients treated with an SSRI or related drug, and 4510 treated with an alternative antidepressant. The standardised effect size for SSRIs and related drugs together versus alternative antidepressants using a fixed effects model was 0. 035 (95% CI -0.006 to 0.076; Q = 149.25, df = 97, p < 0.001). REVIEWER'S CONCLUSIONS: There are no clinically significant differences in effectiveness between selective serotonin reuptake inhibitors and tricyclic antidepressants. Treatment decisions need to be based on considerations of relative patient acceptability, toxicity and cost.

Effects of acetate on facultative autotrophy in Chlamydomonas reinhardtii assessed by photosynthetic measurements and stable isotope analyses.

The green alga Chlamydomonas reinhardtii can grow photoautotrophically utilizing CO(2), heterotrophically utilizing acetate, and mixotrophically utilizing both carbon sources. Growth of cells in increasing concentrations of acetate plus 5% CO(2) in liquid culture progressively reduced photosynthetic CO(2) fixation and net O(2) evolution without effects on respiration, photosystem II efficiency (as measured by chlorophyll fluorescence), or growth. Using the technique of on-line oxygen isotope ratio mass spectrometry, we found that mixotrophic growth in acetate is not associated with activation of the cyanide-insensitive alternative oxidase pathway. The fraction of carbon biomass resulting from photosynthesis, determined by stable carbon isotope ratio mass spectrometry, declined dramatically (about 50%) in cells grown in acetate with saturating light and CO(2). Under these conditions, photosynthetic CO(2) fixation and O(2) evolution were also reduced by about 50%. Some growth conditions (e.g. limiting light, high acetate, solid medium in air) virtually abolished photosynthetic carbon gain. These effects of acetate were exacerbated in mutants with slowed electron transfer through the D1 reaction center protein of photosystem II or impaired chloroplast protein synthesis. Therefore, in mixotrophically grown cells of C. reinhardtii, interpretations of the effects of environmental or genetic manipulations of photosynthesis are likely to be confounded by acetate in the medium.

Mutations altering the predicted secondary structure of a chloroplast 5' untranslated region affect its physical and biochemical properties as well as its ability to promote translation of reporter mRNAs both in the Chlamydomonas reinhardtii chloroplast and in Escherichia coli.

Random mutations were generated in the sequence for the 5' untranslated region (5'UTR) of the Chlamydomonas reinhardtii chloroplast rps7 mRNA by PCR, the coding sequence for the mutant leaders fused upstream of the lacZ' reporter in pUC18, and transformed into Escherichia coli, and white colonies were selected. Twelve single base pair changes were found at different positions in the rps7 5'UTR in 207 white colonies examined. Seven of the 12 mutant leaders allowed accumulation of abundant lacZ' message. These mutant rps7 leaders were ligated into an aadA expression cassette and transformed into the chloroplast of C. reinhardtii and into E. coli. In vivo spectinomycin-resistant growth rates and in vitro aminoglycoside adenyltransferase enzyme activity varied considerably between different mutants but were remarkably similar for a given mutant expressed in the Chlamydomonas chloroplast and in E. coli. The variable effect of the mutants on aadA reporter expression and their complete abolition of lacZ' reporter expression in E. coli suggests differences in the interaction between the 5'UTR of rps7 and aadA or lacZ' coding regions. Several rps7 5'UTR mutations affected the predicted folding pattern of the 5'UTR by weakening the stability of stem structures. Site-directed secondary mutations generated to restore these structures in the second stem suppressed the loss of reporter activity caused by the original mutations. Additional site-directed mutations that were predicted to further strengthen (A-U-->G-C) or weaken (G-C-->A-U) the second stem of the rps7 leader both resulted in reduced reporter expression. This genetic evidence combined with differences between mutant and wild-type UV melting profiles and RNase T1 protection gel shifts further indicate that the predicted wild-type folding pattern in the 5'UTR is likely to play an essential role in translation initiation.

Incidence of cancer in primary biliary cirrhosis: the Mayo experience.

Patients with primary biliary cirrhosis (PBC) may be at increased risk for malignancies. Several studies have addressed the risk of specific malignancies; however, there is little information about overall incidences of malignancies in these patients. We hypothesize that these patients may be at an increased risk for cancer. We performed a retrospective chart review evaluating patients with the diagnosis of PBC and malignancies. We reviewed records of patients with PBC presenting to the Mayo Clinic between 1976 and 1985. The diagnosis of PBC was made using evidence of cholestasis, positive antimitochondrial antibody titers and liver biopsy findings consistent with PBC. The incidence of malignancies were then compared with published data by the Surveillance, Epidemiology and End Results (SEER) program of the National Cancer Institute. Of the 1,692 patients with PBC in the Mayo Clinic data base, 114 patients were identified with primary cancer. The number of malignancies was higher than would be anticipated by chance alone; with 93 observed versus 62.4 expected events (P <.001). Hepatobiliary malignancies had a relative risk of 46 (P <.0001) for women and 55 (P <.0001) in men. There was a dramatic increased risk for development of hepatobiliary malignancies. PBC patients might benefit from more aggressive surveillance for hepatobiliary malignancies during their lifetime.

The ratio of aspartate aminotransferase to alanine aminotransferase: potential value in differentiating nonalcoholic steatohepatitis from alcoholic liver disease.

OBJECTIVE: The ratio of aspartate aminotransferase (AST) to alanine aminotransferase (ALT) is often greater than 2:1 in alcoholic hepatitis. The purpose of this study was to determine whether this ratio may be used to distinguish nonalcoholic steatohepatitis (NASH) from alcoholic liver disease. METHODS: Patients with NASH were matched with controls with alcoholic liver disease based on age, gender, and date of diagnosis. The diagnosis of alcoholic liver disease was based on exclusion of other causes and a significant history of alcohol consumption. The diagnosis of nonalcoholic steatohepatitis was based on exclusion of other causes of liver disease and a liver biopsy showing > 10% steatosis and inflammation. The two sided Student t test was used for statistical analysis. RESULTS: From 1990 to 1996, 70 patients with NASH were matched with 70 subjects with alcoholic liver disease. Patients with NASH had a mean AST to ALT ratio of 0.9 (range 0.3-2.8, median 0.7) and subjects with alcoholic liver disease a mean ratio of 2.6 (range 1.1-11.2, median 2.0). The mean AST levels were 66 U/L and 152 U/L, and the mean ALT levels 91 U/L and 70 U/L, in the nonalcoholic steatohepatitis and alcoholic liver disease groups, respectively. Although the absolute aminotransferase levels were significantly different in the two groups (p < 0.05), the greatest difference was observed in the AST to ALT ratio (p < 0.000001). Subset analysis of patients with NASH revealed mean AST to ALT ratios of 0.7, 0.9, and 1.4 for subjects with no fibrosis, mild fibrosis, or cirrhosis, respectively. The differences among these ratios were statistically significant (p < 0.05). CONCLUSIONS: The AST to ALT ratio appears to be a useful index for distinguishing nonalcoholic steatohepatitis from alcoholic liver disease. Although values < 1 suggest NASH, a ratio of > or = 2 is strongly suggestive of alcoholic liver disease.

Isolation and characterization of a mutant protoporphyrinogen oxidase gene from Chlamydomonas reinhardtii conferring resistance to porphyric herbicides.

In plant and algal cells, inhibition of the enzyme protoporphyrinogen oxidase (Protox) by the N-phenyl heterocyclic herbicide S-23142 causes massive protoporphyrin IX accumulation, resulting in membrane deterioration and cell lethality in the light. We have identified a 40.4 kb genomic fragment encoding S-23142 resistance by using transformation to screen an indexed cosmid library made from nuclear DNA of the dominant rs-3 mutant of Chlamydomonas reinhardtii. A 10.0 kb HindIII subclone (Hind10) of this insert yields a high frequency of herbicide-resistant transformants, consistent with frequent non-homologous integration of the complete RS-3 gene. A 3.4 kb XhoI subfragment (Xho3.4) yields rare herbicide-resistant transformants, suggestive of homologous integration of a portion of the coding sequence containing the mutation. Molecular and genetic analysis of the transformants localized the rs-3 mutation conferring S-23142 resistance to the Xho3.4 fragment, which was found to contain five putative exons encoding a protein with identity to the C-terminus of the A rabidopsis Protox enzyme. A cDNA clone containing a 1698 bp ORF that encodes a 563 amino acid peptide with 51% and 53% identity to Arabidopsis and tobacco Protox I, respectively, was isolated from a wild-type C. reinhardtii library. Comparison of the wild-type cDNA sequence with the putative exon sequences present in the mutant Xho3.4 fragment revealed a G-->A change at 291 in the first putative exon, resulting in a Val-->Met substitution at a conserved position equivalent to Val-389 of the wild-type C. reinhardtii cDNA. A sequence comparison of genomic Hind10 fragments from C. reinhardtii rs-3 and its wild-type progenitor CC-407 showed this G-->A change at the equivalent position (5751) within exon 10.

Biophysical, biochemical, and physiological characterization of Chlamydomonas reinhardtii mutants with amino acid substitutions at the Ala251 residue in the D1 protein that result in varying levels of photosynthetic competence.

The QB binding site of the D1 reaction center protein, located within a stromal loop between transmembrane helices IV and V formed by residues Ile219 to Leu272, is essential for photosynthetic electron transport through photosystem II (PSII). We have examined the function of the highly conserved Ala251 D1 residue in this domain in chloroplast transformants of Chlamydomonas reinhardtii and found that Arg, Asp, Gln, Glu, and His substitutions are nonphotosynthetic, whereas Cys, Ser, Pro, Gly, Ile, Val, and Leu substitutions show various alterations in D1 turnover, photosynthesis, and photoautotrophic growth. The latter mutations reduce the rate of QA to QB electron transfer, but this is not necessarily rate-limiting for photoautotrophic growth. The Cys mutant divides and evolves O2 at wild type rates, although it has slightly higher rates of D1 synthesis and turnover and reduced electron transfer between QA and QB. O2 evolution, D1 synthesis, and accumulation in the Ser, Pro, and Gly mutants in high light is reduced, but photoautotrophic growth rate is not affected. In contrast, the Ile, Val, and Leu mutants are impaired in photoautotrophic growth and photosynthesis in both low and high light and have elevated rates of D1 synthesis and degradation, but D1 accumulation is normal. While rates of synthesis/degradation of the D1 protein are not necessarily correlated with alterations in specific parameters of PSII function in these mutants, bulkiness of the substituted amino acids is highly correlated with the dissociation constant for QB in the seven mutants examined. These observations imply that the Ala251 residue plays a key role in D1 protein.

Shine-Dalgarno-like sequences are not required for translation of chloroplast mRNAs in Chlamydomonas reinhardtii chloroplasts or in Escherichia coli.

Initiation of translation in Escherichia coli and related eubacteria involves well-defined interactions between a conserved Shine-Dalgarno (SD) sequence immediately upstream of the initiation codon in the mRNA leader and an equally conserved anti-SD sequence at the 3' end of the 16S rRNA. SD-like sequences found in the leaders of many, but not all, mRNAs from cyanobacteria and chloroplasts are hypervariable in location, size, and base composition compared to those in E. coli, while anti-SD sequences in the respective 16S rRNAs remain highly conserved. We have examined the function of the SD-like sequences found in the leaders of four chloroplast genes of the green alga Chlamydomonas reinhardtii using replacement mutagenesis to eliminate complementarity with the anti-SD sequences and insertion of canonical SD sequences (GGAGG) at positions -9 to -5 relative to the initiation codon. Promoter-leader regions of the atpB, atpE, rps4, and rps7 genes representing the diversity of chloroplast SD-like sequences were fused to aadA and uidA reporter genes encoding spectinomycin resistance and GUS activity respectively. Analysis of chloroplast transformants of C. reinhardtii and transformants of E. coli carrying the wild-type and mutant reporter constructs revealed that mutagenic replacement of the putative SD sequences had no effect on the expression of either the aadA or uidA reporter genes. Chloroplast transformants with the canonical SD sequence also showed no differences in reporter gene expression, whereas expression of the reporter genes was increased by 10 to 30% in the E. coli transformants. Collectively our results suggest that even though SD-dependent initiation predominates in E. coli, this bacterium also has the capacity to initiate translation by an SD-independent mechanism. In contrast, plant chloroplasts, and very probably their cyanobacterial ancestors, appear to have adopted the SD-independent mechanism for translational initiation of most mRNAs.