Cutting seton for the treatment of cryptoglandular fistula-in-ano: a systematic review and meta-analysis.

BACKGROUND: The use of cutting seton (CS) for the management of cryptoglandular fistula-in-ano has remained controversial because of reports of fecal incontinence, postoperative pain, and extended healing time. The aim of this review was to provide the first synthesis of studies investigating the use of CS for the treatment of cryptoglandular fistula-in-ano. METHODS: MEDLINE, Embase, and CENTRAL were searched up to October 2022. Randomized controlled trials and observational studies comparing CS with alternative interventions were included, along with single-arm studies evaluating CS alone. The primary outcome was fistula-in-ano recurrence, and secondary outcomes included incontinence, healing time, proportion with complete healing, and postoperative pain. Inverse variance random-effects meta-analyses were used to pool effect estimates. RESULTS: After screening 661 citations, 29 studies were included. Overall, 1513 patients undergoing CS (18.8% female, mean age: 43.1 years) were included. Patients with CS had a 6% (95% CI: 3-12%) risk of recurrence and a 16% (95% CI: 5-38%) risk of incontinence at 6 months. CS patients had an average healing time of 14.6 weeks (95% CI: 10-19 weeks) with 73% (95% CI: 48-89%) of patients achieving complete healing at 6 months postoperatively. There was no difference in recurrence between CS and fistulotomy, advancement flap, two-stage seton fistulotomy, or draining seton. CONCLUSIONS: Overall, this analysis shows that CS has comparable recurrence and incontinence rates to other modalities. However, this may be at the expense of more postoperative pain and extended healing time. Further comparative studies between CS and other modalities are warranted.

Differences in in-hospital outcomes and healthcare utilization for laparoscopic versus open approach for emergency inguinal hernia repair: a nationwide analysis.

PURPOSE: There has been a growing debate of whether laparoscopic or open surgical techniques are superior for inguinal hernia repair. For incarcerated and strangulated inguinal hernias, the laparoscopic approach remains controversial. This study aims to be the first nationwide analysis to compare clinical and healthcare utilization outcomes between laparoscopic and open inguinal hernia repair in an emergency setting. METHODS: A retrospective analysis of the National Inpatient Sample was performed. All patients who underwent laparoscopic inguinal hernia repair (LIHR) and open inguinal hernia repair (OIHR) between October 2015 and December 2019 were included. The primary outcome was mortality, and secondary outcomes include post-operative complications, ICU admission, length of stay (LOS), and total admission cost. Two approaches were compared using univariate and multivariate logistic and linear regression. RESULTS: Between the years 2015 and 2019, 17,205 patients were included. Among these, 213 patients underwent LIHR and 16,992 underwent OIHR. No difference was observed between laparoscopic and open repair for mortality (odds ratio [OR] 0.80, 95% CI [0.25, 2.61], p = 0.714). Additionally, there was no significant difference between groups for post-operative ICU admission (OR 1.11, 95% CI [0.74, 1.67], p = 0.614), post-operative complications (OR 1.09, 95% CI [0.76, 1.56], p = 0.647), LOS (mean difference [MD]: -0.02 days, 95% CI [- 0.56, 0.52], p = 0.934), or total admission cost (MD: $3,028.29, 95% CI [$- 110.94, $6167.53], p = 0.059). CONCLUSION: Laparoscopic inguinal hernia repair is comparable to the open inguinal hernia repair with respect to low rates of morbidity, mortality as well as healthcare resource utilization.

Targeted metabolomics reveals reduced levels of polyunsaturated choline plasmalogens and a smaller dimethylarginine/arginine ratio in the follicular fluid of patients with a diminished ovarian reserve.

STUDY QUESTION: Does the metabolomic profile of the follicular fluid (FF) of patients with a diminished ovarian reserve (DOR) differ from that of patients with a normal ovarian reserve (NOR)? SUMMARY ANSWER: The metabolomic signature of the FF reveals a significant decrease in polyunsaturated choline plasmalogens and methyl arginine transferase activity in DOR patients compared to NOR patients. WHAT IS KNOWN ALREADY: The composition of the FF reflects the exchanges between the oocyte and its microenvironment during its acquisition of gametic competence. Studies of the FF have allowed identification of biomarkers and metabolic pathways involved in various pathologies affecting oocyte quality, but no large metabolomic analysis in the context of ovarian ageing and DOR has been undertaken so far. STUDY DESIGN, SIZE, DURATION: This was an observational study of the FF retrieved from 57 women undergoing in vitro fertilization at the University Hospital of Angers, France, from November 2015 to September 2016. The women were classified in two groups: one including 28 DOR patients, and the other including 29 NOR patients, serving as controls. PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients were enrolled in the morning of oocyte retrieval after ovarian stimulation. Once the oocytes were isolated for fertilization and culture, the FF was pooled and centrifuged for analysis. A targeted quantitative metabolomic analysis was performed using high-performance liquid chromatography coupled with tandem mass spectrometry, and the Biocrates Absolute IDQ p180 kit. The FF levels of 188 metabolites and several sums and ratios of metabolic significance were assessed by multivariate and univariate analyses. MAIN RESULTS AND THE ROLE OF CHANCE: A total of 136 metabolites were accurately quantified and used for calculating 23 sums and ratios. Samples were randomly divided into training and validation sets. The training set, allowed the construction of multivariate statistical models with a projection-supervised method, i.e. orthogonal partial least squares discriminant analysis (OPLS-DA), applied to the full set of metabolites, or the penalized least absolute shrinkage and selection operator with logistic regression (LASSO-LR), applied to the ratios and sums of the metabolites. Both multivariate models showed good predictive performances when applied to the validation set. The final penalized model retained the three most significant variables, i.e. the total dimethylarginine-to-arginine ratio (Total DMA/Arginine), the sum of the polyunsaturated choline plasmalogens (PUFA ae), and the patient's age. The negative coefficients of Total DMA/Arginine and PUFA ae indicated that these FF variables had lower values in DOR patients than in NOR patients. LARGE SCALE DATA: N/A. LIMITATIONS REASONS FOR CAUTION: This study presents two limitations. First, with this targeted metabolomics analysis, we have explored only a limited portion of the FF metabolome. Second, although the signature found was highly significant, the mechanism underlying the dysfunction remains undetermined. WIDER IMPLICATIONS OF THE FINDINGS: The understanding of the mechanisms implied in ovarian ageing is essential for providing an adequate response to affected women desiring pregnancy. Our study proposes an incoming signature that may open new paths towards this goal. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the University Hospital of Angers, the University of Angers, and the French national research centers, INSERM and the CNRS. There were no competing interests.

Stakeholder attitudes towards the role and application of informed consent for newborn bloodspot screening: a study protocol.

INTRODUCTION: Newborn bloodspot screening (NBS) involves testing a small sample of blood taken from the heel of the newborn for a number of serious and life-limiting conditions. In Canada, newborn screening programmes fall under provincial and territorial jurisdiction with no federal coordination. To date, we know very little about the underlying beliefs around different consent practices or how terminology is interpreted by different individuals. Differences in attitudes may have important healthcare consequences. This study will provide empirical data comparing stakeholder opinions on their understanding of consent-related terminology, the perceived applicability of different consent approaches to newborn screening, and the requirements of these different approaches. METHODS AND ANALYSIS: Parents, healthcare professionals and policymakers will be recruited in the provinces of Ontario and Newfoundland and Labrador. Parents will be identified through records held by each provincial screening programme. Healthcare professionals will be purposively sampled on the basis of engagement with newborn screening. Within each province we will identify policymakers who have policy analysis or advisory responsibilities relating to NBS. Data collection will be by qualitative interviews. We will conduct 20 interviews with parents of young children, 10 interviews with key healthcare professionals across the range of appropriate specialties and 10 with policymakers at each site (40 per site, total, N=80). The examination of the transcripts will follow a thematic analysis approach. Recruitment started in June 2014 and is expected to be complete by June 2015. ETHICS AND DISSEMINATION: This study received ethics approval from the Ottawa Health Science Network Research Ethics Board, the Children's Hospital of Eastern Ontario Research Ethics Board (both Ontario), and the Health Research Ethics Authority (Newfoundland and Labrador). RESULTS: These will be reported in peer-reviewed publications and conference presentations. The results will have specific application to the development of parent education materials for newborn screening.

Glycine receptors in a population of adult mammalian cones.

Glycinergic interplexiform cells provide a feedback signal from the inner retina to the outer retina. To determine if cones receive such a signal, glycine was applied on cultured porcine cone photoreceptors recorded with the patch clamp technique. A minor population of cone photoreceptors was found to generate large currents in response to puff application of glycine. These currents reversed close to the calculated equilibrium potential for chloride ions. These glycine-elicited currents were sensitive to strychnine but not to picrotoxin consistent with the expression of alpha-beta-heteromeric glycine receptors. Glycine receptors were also activated by taurine and beta-alanine. The glycine receptor antibody mAb4a labelled a minority of the cone photoreceptors identified by an antibody specific for cone arrestin. Finally, expression of the beta subunit of the glycine receptor was demonstrated by single cell RT-PCR in a similar proportion (approximately 13%) of cone photoreceptors freshly isolated by lectin-panning. The identity of cone photoreceptors was assessed by their specific expression of the cone arrestin mRNA. The population of cone photoreceptors expressing the glycine receptor was not correlated to a specific colour-sensitive subtype as demonstrated by single cell RT-PCR experiments using primers for S opsin, cone arrestin and glycine receptor beta subunit. This glycine receptor expression in a minority of cones defines a new cone population suggesting an unexpected role for glycine in the visual information processing in the outer retina.

Control of Listeria monocytogenes in raw-milk cheeses.

The development of Listeria monocytogenes in cheeses made with raw-milk originating from six different farms and according to the Saint-Nectaire cheesemaking technology was studied. Milk was inoculated with two strains of L. monocytogenes at 5 to 10 CFU/25 ml. Microbial and chemical analyses were carried out at appropriate intervals during ripening. L. monocytogenes did not grow in the cores of cheeses prepared with milk originating from three farms. That inhibition could be partially attributed to the pH values and L-lactate content. There was no growth in cheeses with pH below 5.2 and lactate content around 14 mg/g. In all cheeses, L. monocytogenes stopped growing in the cores of cheeses after eight days and some other factors may be involved in the inhibition. No relation was found between L. monocytogenes count and other microbial counts. Growth occurred on cheese surfaces between eight and eighteen days, when the pH significantly increased. The lowest L. monocytogenes growth was found on the surface of cheeses with the lowest pH and without any core growth. Further studies will be performed to clarify the involvement of the microbial community in L. monocytogenes inhibition, in particular during the ripening period.

Advanced glycation end products can induce glial reaction and neuronal degeneration in retinal explants.

BACKGROUND/AIMS: Neuronal degeneration has been reported to occur in diabetic retinopathy before the onset of detectable microvascular abnormalities. To investigate whether advanced glycation end products (AGE) could be directly responsible for retinal neurodegeneration, retinal explants were incubated with glycated bovine serum albumin (BSA). METHODS: Retinal explants obtained from non-diabetic adult rats were incubated 4 days with or without 200 mug/ml glycated BSA. Neural apoptosis was quantified by terminal dUTP nick end labelling (TUNEL) binding and immunostaining with anti-cleaved caspase-3 antibody. Expression of glial fibrillary acidic protein (GFAP) was localised by immunofluorescence. RESULTS: TUNEL and cleaved caspase-3 positive cells increased significantly by 2.2-fold and 2.5-fold in retinal explants incubated in glycated BSA (p<0.05), respectively. The ganglion cell layer was the most sensitive retinal layer to the glycated BSA. Neuronal degeneration was confirmed by the increased GFAP labelling in Müller glial cells from retinal explants treated with glycated BSA. CONCLUSION: These results suggest that AGE could induce retinal neurodegeneration in the absence of blood perfusion. Cells in the ganglion cell layer appeared to be the most sensitive as in diabetic retinopathy and its animal models. AGE toxicity could therefore contribute to the early pathological mechanisms of diabetic retinopathy.

Diversity, dynamics and activity of bacterial populations in 'Registered Designation of Origin' Salers cheese by single-strand conformation polymorphism analysis of 16S rRNA genes.

AIMS: The aim of this work was to measure the dynamic global metabolic activities of the microbial community during ripening of RDO Salers cheese by using a direct molecular approach. METHODS AND RESULTS: A culture-independent approach including PCR, reverse transcriptase PCR (RT-PCR) and single strand conformation polymorphism (SSCP) analysis of 16S rRNA genes was applied on 'Registered Designation of Origin' Salers cheese samples collected in three farms. The evolution of the global structure of the microbial community in terms of structure or global activities was assessed using ecological indices. The diversity of the global population was higher on RNA patterns than on DNA patterns, because of less dominance and greater richness. Comparison of the SSCP patterns derived from RNA and DNA analysis indicated that the dominant population was not necessarily the most active. The metabolic activities of each bacterial group changed significantly during ripening. Besides lactic acid bacteria that were dominant on both DNA and RNA patterns, the dynamics of the presence and activity of microbial groups rarely studied in the core of cheese, such as corynebacteria, or of unidentified peaks were reported. CONCLUSIONS: By using SSCP RNA analysis, we were able to obtain information about the activity of bacterial population in cheese, which varied a lot between cheeses and was changing perpetually during ripening. SIGNIFICANCE AND IMPACT OF THE STUDY: Double DNA-RNA SSCP analysis opens up future prospects in the microbial ecology of cheeses. It will have many applications for controlling of microbial community during cheese processing.

Separation and purification of benzylpenicillin produced by fermentation using coupled ultrafiltration and nanofiltration technologies.

The purpose of this study was to evaluate the capacity of using coupled ultrafiltration-nanofiltration technologies for separation and purification of benzylpenicillin (BP). More specifically, we verified the efficiency of three ultrafiltration (UF) membranes (cut-off of 5000, 30,000 and 100,000 Da) to remove impurities that cause stable emulsion during the chemical extraction of the antibiotic. We also tested the effectiveness of a nanofiltration (NF) membrane (cut-off of 300 Da) to concentrate the benzylpenicillin recovered from permeates and to decrease the osmotic pressure by reducing the ionic charge of the broth. Results have shown that high recovery (89.0-91.0%) can be obtained in permeate generated by the 30,000 and 100,000 UF membranes, but a slight emulsion will be formed during phase separation. With the 5000 UF membrane, lower recovery is obtained (81.0%) but no emulsion is produced, leading to a high solvent extraction yield (94.6%). The nanofiltration of 30,000 and 100,000 UF permeates leads to very high recovery (98.0%), but stable emulsions are formed, reducing the chemical extraction yield (80.0-82.6%). For the nanofiltration of 5000 UF permeate, excellent recovery of the antibiotic is noted (97.4%) leading to high extraction yield (92.4%) with no emulsion formed. Diafiltration step should be applied during UF procedure in order to increase the antibiotic recovery in the generated permeates.

Identification of selenomethionine in selenized yeast using two-dimensional liquid chromatography-mass spectrometry based proteomic analysis.

Selenium-enriched yeast has been commonly used as a nutritional supplement. Here we describe a protocol used to investigate the metabolic fate of inorganic selenium in yeast. We provide definitive, mass spectrometry based evidence for the non-specific incorporation of selenomethionine in the yeast proteome involving the replacement of about 30% of all methionine with selenomethionine.

Family affairs.

Abstract The strong bonds that often remain with ex-lovers are a remarkable aspect of lesbian relationships. This poem, written in the early '70s, reveals the complexities of ex-lover relationships with a humorous twist. It represents a time in U.S. American lesbian culture when the dividing lines between friends and lovers were blurred and the personal/political aspects of non-monogamy were being explored.

Analysis of Euglena gracilis alpha-, beta- and gamma-tubulin genes: introns and pre-mRNA maturation.

We have cloned and analyzed alpha-, beta- and gamma-tubulin genes from Euglena gracilis. The gamma-tubulin genes are 6-10 times longer than the alpha- and beta-tubulin genes, owing to the presence of numerous introns. These introns are all of the conventional type, whereas the alpha- and beta-tubulin genes contain both conventional and non-conventional introns. This is the first time that both types of introns have been found in the same gene. In the E. gracilis genome there are two genes for each tubulin, but the level of gamma-tubulin mRNA is 60 times lower than that of alpha- and beta-tubulin RNAs. The distinctive structure of gamma-tubulin genes prompted us to investigate the maturation of its pre-mRNA. We show that trans-splicing occurs before the cis-splicing of the first intron of the pre-mRNA and that polyadenylation occurs after the cis-splicing of the last intron of the pre-mRNA. We propose that mRNA processing is likely to play a role in regulating the amounts of different tubulins in E. gracilis.

[Impact of the climatic scenario of global warming on the growth of trees]. / Impact d'un scénario climatique de réchauffement global sur la croissance des arbres.

The climatic impact on tree radial growth resulting from an atmospheric CO2 doubling was studied for 24 populations of five tree species in the French Alps and the French Mediterranean area. The Arpege AGCM, which predicts a 3 degrees C increase in mean temperature and a light increase of precipitation, is used to estimate the climatic perturbation. The method is based on the integration of estimated climate in an empirical tree-ring to climate model, involving artificial neural networks. Only a few populations are sensitive to the climatic change; all are located on the boundaries of their ecological area and can be divided in two groups. The first one is composed of high altitude populations which show a growth increase induced by the warmer climate during the growing season. The second one, composed of a single Mediterranean Scots pine population, reacts with a severe growth reduction induced by the stronger water stress in summer.

Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae), a potential indicator of chronic toxicity of malathion (organophosphate insecticide).

A laboratory study on the sublethal effects of malathion on the net-spinning behavior of the caddisfly larvae Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to organophosphorus insecticides. Two anomalies were identified after chronic exposure to 0.01, 0.05, 0.1, 0.5 and 1.0 µg l(-1) malathion. The first was a distortion of the midline meshes where the normal diamond shape structure was disrupted and the meshes were separated by extra strands (called 'midline' anomaly). The second aberration observed was a significant decrease in net symmetry. Both anomalies were highly correlated to the toxic action of malathion, i.e. inhibition of the acetylcholinesterase enzyme (AChE). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses of capture nets did not show any modification of silk polypeptides after exposure to malathion, indicating that net distortions were not related to silk composition. Both anomalies seem to represent the symptoms of the specific toxic action of malathion; nevertheless, they can serve as an index of the physiological condition of the larvae, especially the midline anomaly. The symmetry of the nets decreased significantly after exposure to 0.5 and 1.0 µg l(-1). However, the toxicity curves (EC(50)) showed that the sensitivity threshold for the midline anomaly ranged from 0.11 to 0.28 µg l(-1), which reflect more realistic exposure to concentrations expected to occur in the field. Hence, the use of capture net anomalies of hydropsychid larvae could represent a valuable indicator of sublethal toxicity induced by malathion and other organophosphorus insecticides in running waters.

Effects of 2,4-dichlorophenol on the net-spinning behavior of hydropsyche slossonae larvae (Trichoptera; Hydropsychidae), an early warning signal of chronic toxicity.

In order to assess the potential of hydropsychid capture net anomalies as a bioindicator of chronic toxicity in streams and rivers, the effects of 2,4-dichlorophenol (2,4-DCP) exposure on the net-spinning behavior of Hydropsyche slossonae were examined for anomalies after 0, 5, 10, 15, and 20 exposure days to gradient concentration of 2,4-dichlorophenol. The net-spinning behavior was significantly affected when larvae were exposed to 1.0, 10, 25, and 50 microg small middle dotL(-1), as expressed by the occurrence of two distinct abnormalities. The first one was a distortion of the midline meshes, where the normal diamond-shape structure is disrupted and the meshes are separated by extra strands (called "midline anomaly). The second aberration observed was called "chaotic net, where the nets are highly irregular without any real structure or well-defined areas. A good correlation was found between the chaotic net frequencies and the reduction of ATP concentrations in the larvae, indicating possible uncoupling effects of 2,4-DCP on the oxidative phosphorylation process. Toxicity curves demonstrate that the sensitivity threshold of chaotic net frequencies ranged from 3.5 to 7 microg small middle dotL(-1), which is highly sensitive compared with other sublethal effects of 2,4-DCP on other aquatic species.

Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae) following a sublethal chronic exposure to cadmium.

A laboratory study on the sublethal effects of cadmium (Cd) on the net-spinning process of the larvae of Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to Cd. Two major anomalies with different frequency levels were identified after chronic exposure to 0.37, 1.2, 11.6, 21.4 and 43.3 microg l(-1) of Cd. The first was a distortion of the midline meshes where the diamond-shape structure is disrupted and the meshes are separated by extra strands (called 'midline' anomaly). The second aberration consisted of a distortion of the rectilinear structure of net opening by strands being fused or added over the meshes (called 'crossover' anomaly). The midline distortion may be linked to a physiological stress caused by Cd, which can affect the control of the net-spinning process. It was not possible to relate the crossover aberrations to a specific toxic action of Cd, but data indicated that both anomalies are independent from each other and that two modes of action could be implicated. Protein analyses of capture nets have revealed silk polypeptide modifications at the highest Cd concentration tested, indicating a possible effect of Cd interaction with silk proteins. However, neither a gradient-concentration nor a time-dependent response could be established with both aberration frequencies. Silk protein modifications would rather play a secondary role in the appearance of both net anomalies, and mostly at a high concentration level. Finally, the toxicity curves (EC(50)) show that the sensitivity threshold for both types of aberration ranged from 1 to 5 microg l(-1) which is highly sensitive compared with other sublethal effects of Cd on other macroinvertebrate species. Hence, the use of capture-net anomalies of hydropsychid larvae would represent a valuable indicator of sublethal toxicity induced by Cd and possibly by other metals in running waters.

Mass sensitivity of acoustic plate mode in liquids.

In this paper, the concept of electrical effective permittivity function is used to calculate the eigen-frequencies and the particle displacements of piezoelectric acoustic plate modes (APM). These results allowed us to determine the mass sensitivities of the first order vibration modes using a first order perturbation theory. Theoretical results are discussed and compared to those of a variational method and isotropic two-layer composite analysis in the case of a shear horizontal APM sensor on a singly rotated cut quartz substrate. Experimental measurements by a copper electrodeposition are carried out and show that the perturbation method leads to a better understanding of the APM behavior.

The cox1 gene from Euglena gracilis: a protist mitochondrial gene without introns and genetic code modifications.

We present the nucleotide sequence of the cox 1 gene encoding subunit 1 of cytochrome c oxidase in Euglena gracilis, the first report on a mitochondrial gene from this protist. Its study reveals that the Euglena mitochondrial genome does not appear as a compact and homogeneous structure and that its A+T content is high (about 76%) whereas this value is less than 50% in nuclear DNA. The Euglena cox1 gene does not exhibit any intron, and an amino-acid alignment of Euglena COX1 with homologous proteins shows that the universal genetic code is used. Comparisons of the genomic and cDNA sequences of Euglena cox1 indicate that the transcript does not undergo RNA editing as found in trypanosomes and in higher plants. The phylogeny obtained with COX1 protein sequences is in agreement with that obtained with nuclear rRNA sequences and places Euglena and Trypanosoma far apart from other eukaryotes. This result strengthens the hypothesis that these protists represent the earliest mitochondrion-containing organisms.

Comparative performance of piezoceramic and crystal SAW filters.

Bulk elastic, piezoelectric, and dielectric constants of four lead zirconate titanate piezoceramics, Pz24, Pz26, Pz27, Pz28, and a modified lead titanate, PTS, are measured and used to theoretically compute the effective permittivity curve of each material from which the surface acoustic wave (SAW) properties are deduced. In parallel, experimental measurements of the SAW properties are carried out by using a curve fitting algorithm on the real and imaginary parts of the electrical input impedance of an unapodised single electrode SAW transducer. The SAW propagation losses are also measured using a SAW delay line. For these ceramics, the effects of a hot isostatic pressing (HIP) post sintering process on the performances of the device are also studied. All these results are discussed and show that ceramic materials, particularly PTS, have potential for SAW applications.

Structure and expression of Euglena gracilis nuclear rbcS genes encoding the small subunits of the ribulose 1,5-bisphosphate carboxylase/oxygenase: a novel splicing process for unusual intervening sequences?

In the protist Euglena gracilis, the small subunit of the chloroplast enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase is encoded by nuclear rbcS genes and synthesized as a polyprotein precursor containing eight mature small subunit molecules. This large precursor is encoded by at least eight different nuclear genes as ascertained by transcript analysis. The structure of three rbcS genes was established and the coding sequences were found to be interrupted by many intervening sequences (IVS). Apart from the first 5' intron involved in trans-splicing, none of these IVSs obeys the GT-AG rule characteristic of introns in higher eukaryote genes. Surprisingly, these IVSs are located at identical positions within the three genes studied. Moreover, extensive sequence homologies were found between IVSs located in the same gene as well as in different genes. The sequences of these homologous IVSs differ only by inserted and/or deleted sequences. The striking conservation of the 5' and 3' regions of these IVSs is correlated to their potential secondary structures. These structures, which bring the IVS extremities together with the exon boundaries, could be involved in a novel splicing process. The second 5' IVS is shown to be excised before the addition of the spliced leader sequence to the pre-mRNA. Similarly, two 3' IVSs are excised before the polyadenylation step. These results suggest that IVS splicing is faster than eukaryotic genomic cis-splicing and involves components other than those of the classical spliceosomes.