RLR1 (THO2), required for expressing lacZ fusions in yeast, is conserved from yeast to humans and is a suppressor of SIN4.

We isolated a mutation (rlr1-1; required for lacZ RNA) in the Saccharomyces cerevisiae (Sc) RLR1 gene as a suppressor of sin4, a component of the Mediator subcomplex of the RNA polymerase II holoenzyme and a determinant of chromatin structure. RLR1 encodes a deduced protein found also in fission yeast, nematode worms, and humans. The presence of these orthologs suggests that Rlr1 family members comprise a class of putative KEKE motif-containing proteins, characteristic of certain chaperones as well as regulators and subunits of the mammalian 20S proteasome. A role for RLR1 (THO2) in transcription appears to occur at a step subsequent to transcription initiation (see also Piruat, J.I. and Aguilera, A., 1998. EMBO J. 17, 4859-4872); Sc genes fused to the reporter gene lacZ were expressed at a very low level, while the corresponding native chromosomal genes were expressed at approximately normal levels in rlr1 mutants. Our studies show that rlr1 mutations cause a wide range of growth defects in addition to their novel affect on lacZ.

A comparison of methods of benchmark-dose estimation for continuous response data.

Methods of quantitative risk assessment for toxic responses that are measured on a continuous scale are not well established. Although risk-assessment procedures that attempt to utilize the quantitative information in such data have been proposed, there is no general agreement that these procedures are appreciably more efficient than common quantal dose-response procedures that operate on dichotomized continuous data. This paper points out an equivalence between the dose-response models of the nonquantal approach of Kodell and West and a quantal probit procedure, and provides results from a Monte Carlo simulation study to compare coverage probabilities of statistical lower confidence limits on dose corresponding to specified additional risk based on applying the two procedures to continuous data from a dose-response experiment. The nonquantal approach is shown to be superior, in terms of both statistical validity and statistical efficiency.

Modeling the impact of HIV on the spread of tuberculosis in the United States.

Tuberculosis (TB) was thought to be safely in decline in the United States in the mid-1980s because the number of cases had dropped by 74% between 1953 and 1985. An increase in TB cases was reported, however, in 1986, and an upward trend in TB incidence has continued. The turnaround in TB is well correlated with the rise of the HIV (human immunodeficiency virus) epidemic. The purpose of this work is to investigate, through the use of mathematical models, the magnitude and duration of the effect that the HIV epidemic may have on TB. Models are developed which reflect the transmission dynamics of both TB and HIV, and the relative merits of these models are discussed. The models are then linked together to form a model for the combined spread of both diseases. A numerical study is performed to investigate the influence of certain key parameters. The effect that HIV will have on the general population is found to be dependent on the contact structure between the general population and the HIV risk groups, as well as a possible shift in the dynamics associated with TB transmission.

Models for the simple epidemic.

Stochastic and deterministic models for the simple epidemic are formulated and compared. Both discrete and continuous time models are considered. The conjecture of equivalence between stochastic and deterministic models for large initial susceptible populations is shown to be of limited practical importance by a simulation study, whereas the number of initial infectives is shown to dramatically affect the convergence of the two types of models. In addition, the discrete stochastic model, which is easy to formulate and simulate, is shown to converge with its continuous counterpart as the time step becomes small.

The effect of color on light-induced seizures: a case report.

BACKGROUND: Two to four percent of epileptics have their seizures triggered by flickering light, an effect which may be wavelength-dependent. We evaluated a patient with a long-standing history of light-induced petit mal seizures to determine if the seizures were triggered more effectively by a particular range of wavelengths and to determine whether this information could be used in the optometric management of such patients. METHODS: Flickering lights of different wavelengths but equal luminance were presented while the patient's electroencephalogram (EEG) and subjective reports were monitored. RESULTS: The EEG results were not significantly different for different wavelengths, but the patient reported that longer wavelength light induced stronger seizures more consistently. Based on these results we concluded that the patient might benefit from spectacles tinted to exclude transmission of red light. The patient was given 4 pairs of 85% transmission spectacles, which differed only in lens tint (red, yellow, green, and blue), to try over a period of time. The patient felt that the tinted lenses were not dark enough to decrease his seizures effectively and he has opted to wear standard sunglasses. CONCLUSIONS: We feel this case shows that patients with light-induced seizures can benefit from optometric consultation. Because the patient's subjective report identified the clearest wavelength effect, we feel that it is reasonable for the general practitioner to suggest deeply tinted lenses to reduce the frequency of seizures in these patients.

Sequence of the Saccharomyces cerevisiae YTP1 gene encoding a deduced novel type-III integral membrane protein with domains of sequence similarity to mitochondrial electron-transport enzymes.

The nucleotide sequence is reported for the Saccharomyces cerevisiae YTP1 (yeast putative transmembrane (TM) protein) gene, encoding a novel deduced protein of 459 amino acids (aa) in length (51 643 Da). The Ytp1 protein appears by computer analysis (hydropathy plots in conjunction with the combined predictions of several Internet on-line programs that deduce protein structure from primary sequence data) to be a type-III integral TM protein containing 10 or 11 TM-spanning domains. Blocks of aa sequence similarity, predominantly to mitochondrial electron transport proteins, are consistent with the notion that Ytp1 is an integral TM protein and may reflect some aspect of its functional role. The C terminus of Ytp1 is both hydrophilic and highly negatively charged, with 11 of the last 33 aa corresponding to Glu or Asp. Although Northern blot analysis indicates that this gene is expressed, a disruption of YTP1 shows that it is not essential. YTP1 is located between SIN4 (TSF3) and KEX2 (SRB1) at position 205 (kb) on the chromosome XIV physical map.

Neoplastic transformation of neonatal human fibroblasts exposed in vitro to radiation from a quartz-halogen lamp.

The use of unfiltered quartz-halogen lamps exposes human skin to radiation that spans much of the ultraviolet (UV) spectrum. Reports indicate that exposure to quartz-halogen lamps is erythemogenic, mutagenic, and carcinogenic. To compare the carcinogenic potential of quartz-halogen lamps with that of other UV sources, we determined the dose dependence for cytotoxicity and neoplastic transformation in neonatal human fibroblasts exposed in vitro to: a 15 W germicidal lamp (primarily 254 nm radiation), a 15 W Cool White fluorescent lamp, and an unfiltered 20 W quartz-halogen lamp. Fluence-survival relationships were multiphasic with linear dose response below about 40% survival, and all three sources produced fluence-dependent transformation as indicated by induction of anchorage-independent growth. Maximum transformation frequencies were observed at fluences of 5-8 J/m2 for the germicidal lamp, 6.3 kJ/m2 for the fluorescent lamp, and 300 J/m2 for the quartz-halogen lamp. These data confirm the carcinogenic potential of the quartz-halogen lamp.

Study of sodium saccharin co-carcinogenicity in the rat.

A co-carcinogenicity experiment was conducted with female Sprague-Dawley rats in which the effects of short-term sodium saccharin dosing and initiation with a direct-acting carcinogen were examined in the urinary bladder. All initiated animals were administered 0.5 mg N-methyl-N-nitrosourea (MNU) by instillation into the bladder at 8 wk of age. The animals were also given saccharin at one of four levels in the diet (0, 1.0, 2.5 or 5%) for 4 wk either (1) just before treatment with MNU (4-8 wk of age), (2) centred on treatment with MNU (6-10 wk of age) or (3) after MNU treatment (8-12 wk of age). Additionally, a group of animals was exposed to saccharin through the milk for 3 wk by dosing the mothers, starting on the day of parturition. The animals were held on control diet until interim killing of 20 animals per group at about 590 days of age, removal for morbidity, or terminal killing of the remainder of 60 animals per treatment around 780 days of age. A histopathological examination was made of the urinary tract and the relationship of saccharin dose to bladder tumour prevalence analysed statistically. A consistent increase (with very weak statistical significance) in tumour rate at interim killing, and for the pathology data overall, was shown by the 2.5% dose group given saccharin from 8 to 12 wk of age. Tumour prevalences of 47.6 and 40.7% v. control prevalences of 21.1 and 25.4% were observed for the two time periods (P values < 0.076 and < 0.0853, respectively). All groups given saccharin neonatally showed increased tumour prevalence for both time periods, but none of the differences was statistically significant at the 95% confidence level. No consistent increase in tumour prevalence was seen in the groups given saccharin from 4 to 8 or 6 to 10 wk of age; thus, these data suggest that saccharin does not act as a strong co-carcinogen in the MNU-treated rat bladder.

In vitro transformation potential of N-polycyclic aromatic hydrocarbons in rat tracheal epithelial cells.

Nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) are environmental contaminants and potential human airway carcinogens. Agents of this class show a wide range of potencies for toxicity, mutagenicity and carcinogenicity that are associated with the structure of the PAH and the position of the nitro group. In order to evaluate the effect of nitro substitution on in vitro biological activity, the cytotoxicity and transformation potential of two parent PAHs, pyrene and chrysene, and a series of nitro derivatives were examined in the rat tracheal epithelial (RTE) cell system. The nitro derivatives, but not pyrene or chrysene, produced dose-dependent decreases in the colony forming efficiency of the RTE cells. The most cytotoxic agents were 1,6-dinitropyrene and 6-nitrochrysene with ED(50)s of 1.6 mum and 5.9 mum, respectively, followed by 4-nitropyrene and 1-nitropyrene with ED(50)s of 26.3 mum and 44.5 mum, respectively. These compounds were evaluated for transformation potential at three treatment levels that spanned the cytotoxic range, and the assays were scored for morphologically transformed preneoplastic colonies. The control or spontaneous transformation frequency in this series of experiments was 1.79 +/- 0.47 (x 10(-4)). 6-Nitrochrysene and 1,6-dinitropyrene were the only compounds that produced transformation frequencies (12.17 x 10(-4) and 9.68 x 10(-4), respectively) that were statistically different from control. The maximum transformation frequencies of the compounds were compared with published data for liver tumorigenicity in the newborn mouse assay. The orders for tumorigenicity and transformation were the same (1,6-dinitropyrene > 4-nitropyrene > 1-nitropyrene approximately - pyrene and 6-nitrochrysene > chrysene), and the relative potencies of the compounds were similar in the two assays. These results suggest that RTE cells are capable of metabolizing nitro-PAHs to reactive products, and that, within this limited class of compounds, in vitro transformation data in the RTE cell system may be correlated with tumorigenicity in animal studies.

TSF1 to TSF6, required for silencing the Saccharomyces cerevisiae GAL genes, are global regulatory genes.

The Saccharomyces cerevisiae GAL1 and GAL10 genes are controlled in response to the availability of galactose and glucose by multiple activating and repressing proteins bound at adjacent or overlapping sites in UASG. Negative control elements in UASG, designated GAL operators GALO1 to GALO6, are required to silence basal level transcription of GAL1 and GAL10 when galactose is absent. We isolated and characterized recessive mutations in six nuclear genes, TSF1 to TSF6, that impair silencing of GAL1 and GAL10 gene expression. Surprisingly, the results of several experiments suggest that the TSF genes encode global regulatory factors. tsf1 to tsf6 mutations derepressed expression from yeast CYC-GAL hybrid promoters (fused to lacZ) that harbor a variety of operator sequences, and caused pleiotropic defects in cell growth, mating, and sporulation. S1 mapping and Northern blot results for tsf3 suggest that the molecular defect is at the transcriptional level. Mutant phenotypes were additive in certain combinations of tsf double mutants, implying that more than one silencing pathway is involved in TSF1 to TSF6 function. Most significantly, mutations in all six TSF1 to TSF6 genes activated expression from GAL1 and CYC1 promoters (fused to lacZ) lacking upstream activating sequences. Combined, the simplest interpretation of these results is that TSF1 to TSF6 encode factors that control the function of the basic RNA polymerase II transcriptional machinery.

Upper confidence limits on excess risk for quantitative responses.

The definition and observation of clear-cut adverse health effects for continuous (quantitative) responses, such as altered body weights or organ weights, are difficult propositions. Thus, methods of risk assessment commonly used for binary (quantal) toxic responses such as cancer are not directly applicable. In this paper, two methods for calculating upper confidence limits on excess risk for quantitative toxic effects are proposed, based on a particular definition of an adverse quantitative response. The methods are illustrated with data from a dose-response study, and their performance is evaluated with a Monte Carlo simulation study.

TSF3, a global regulatory protein that silences transcription of yeast GAL genes, also mediates repression by alpha 2 repressor and is identical to SIN4.

TSF3 encodes one of six (TSF1 to TSF6) recently identified global negative regulators of transcription in Saccharomyces cerevisiae. Mutant tsf3 strains exhibit defects in transcriptional silencing of the GAL1 promoter, allow expression from upstream activation sequence-less promoters, and exhibit pleiotropic defects in cell growth and development. Here we show that TSF3 is involved in transcriptional silencing mediated by the alpha 2 repressor and demonstrate that specific systems of transcriptional silencing may depend on the more global role of TSF3. Cloning and sequencing of TSF3 allowed us to predict a 974-amino-acid gene product identical to SIN4, a negative regulator of transcription of the HO (homothallism) mating type switching endonuclease. TSF3 disruptions are not lethal but result in phenotypes similar to those of the originally isolated alleles. Our results, together with those of Y. W. Jiang and D. J. Stillman (Mol. Cell. Biol. 12:4503-4514, 1992), suggest that TSF3 (SIN4) affects the function of the basal transcription apparatus, and this effect in turn alters the manner in which the latter responds to upstream regulatory proteins.

Inactivation of a tumor suppressor function in immortal Syrian hamster cells by N-methyl-N'-nitro-N-nitrosoguanidine and by 5-aza-2'-deoxycytidine.

Clonal lines of immortal Syrian hamster cells were previously isolated that either suppressed (supB+) tumorigenicity in hybrids with a malignant hamster cell line (BP6T) or had lost this suppression ability (supB-). Neither line was tumorigenic or showed anchorage-independent growth in normal growth medium. SupB- cells, but not supB+ cells, grew in agar supplemented with the growth factors EGF, PDGF and insulin (EPI), providing a selective assay for the supB- phenotype. After treatment of supB+ cells with either N-methyl-N'-nitro-N-nitrosoguanidine (10-300 ng/ml) or 5-aza-2'-deoxycytidine (25-250 ng/ml), and an expression period of 4-8 weeks, a dose-dependent increase in altered cells that grew in agar supplemented with EPI was observed. Cell lines derived from colonies in agar showed persistent EPI-stimulated growth in agar, and decreased suppression of growth in agar for hybrids with BP6T cells. Thus, carcinogen-induced loss of the tumor suppressor phenotype has been demonstrated.

A case of monocular triplopia of lenticular origin.

A 70-year-old male experienced unilateral monocular triplopia of lenticular origin. The images formed a nearly equilateral triangle and were equally clear. It was noted that the images were formed by sections of the crystalline lens whose borders were parallel to the orientation of the anterior Y-sutures.

Galileo ultraviolet spectrometer experiment: initial venus and interplanetary cruise results.

The Galileo Extreme Ultraviolet Spectrometer obtained a spectrum of Venus atmospheric emissions in the 55.0- to 125.0-nanometer (nm) wavelength region. Emissions of helium (58.4 nm), ionized atomic oxygen (83.4 nm), and atomic hydrogen (121.6 nm), as well as a blended spectral feature of atomic hydrogen (Lyman-beta) and atomic oxygen (102.5 nm), were observed at 3.5-nm resolution. During the Galileo spacecraft cruise from Venus to Earth, Lyman-alpha emission from solar system atomic hydrogen (121.6 nm) was measured. The dominant source of the Lyman-alpha emission is atomic hydrogen from the interstellar medium. A model of Galileo observations at solar maximum indicates a decrease in the solar Lyman-alpha flux near the solar poles. A strong day-to-day variation also occurs with the 27-day periodicity of the rotation of the sun.

Effect of simulated altitude on the visual fields of glaucoma patients and the elderly.

We investigated whether mild hypoxia, such as may be encountered in civilian aircraft, causes temporary visual field defects in elderly persons or temporarily increases pre-existing defects in persons with glaucoma. The central 24-2 program on the Humphrey automated perimeter was used to test visual fields in 3 groups of subjects: 6 with glaucoma; 12 age-matched controls, all of whom were over 44 years of age; and 6 normal subjects under 36 years of age. Visual fields were tested at ground level and at simulated 3000 m (10,000 ft) in an alternating sequence. A repeated measures design of multiple analysis of variance was used to analyze the data. Altitude was found to have no effect on the visual fields of subjects with glaucoma, age-matched normals, or younger subjects. We found no evidence to suggest a change in the present Federal Aviation Administration (FAA) standards, which allow a special certificate to be issued to persons with glaucoma who wish to obtain medical clearance to operate civilian aircraft, nor have we found any evidence that should discourage glaucoma patients from flying as passengers.

The effects of sodium saccharin with and without N-methyl-N-nitrosourea co-treatment on anchorage-independent growth of human diploid fibroblasts.

In order to examine the effects of sodium saccharin on in vitro cell transformation, neonatal human diploid fibroblasts were treated with various levels of the compound during specific phases of a synchronized cell cycle, then subcultured for a suitable expression period, and assayed for anchorage-independent growth in soft agar. The dose-relatedness and cell-cycle-dependency of the effects were determined both in cells treated with sodium saccharin and in cells co-treated with saccharin and the direct-acting carcinogen N-methyl-N-nitrosourea (MNU). Cell treatment with saccharin at ng/ml levels for 10 hr following release from a metabolic block (G(1) phase), with or without MNU treatment (70 mug/ml) at 10 hr, was an effective transforming regimen. Continuous saccharin treatment for 12 days (from the end of the synchronized cell cycle until seeding into soft agar) was often as effective as G(1) exposure, but treatment during the metabolic block or during S-phase and mitosis was always less effective. The dose-relatedness of the effects was similar both for saccharin-induced transformation at ng/ml treatment levels, and for co-transformation with MNU. Maximum colony growth (>100/50,000 seeded cells) was observed at a concentration of 50 ng/ml, and a variable, but decreased, response was seen at higher and lower exposures. MNU co-treatment served to maintain the transformation response at higher (mug/ml) saccharin levels at which saccharin alone was not effective. Thus, sodium saccharin demonstrated significant transforming activity over a wide dose range, both when used alone, and in combination with MNU.

Opposing regulatory functions of positive and negative elements in UASG control transcription of the yeast GAL genes.

The yeast GAL1 and GAL10 genes are transcribed at a remarkably low basal level when galactose is unavailable and are induced by over 4 orders of magnitude when it becomes available. Approximately six negative control elements (designated GAL operators GALO1 to GALO6) are located adjacent to or overlapping four binding sites for the transcription activator GAL4 in the GAL upstream activating sequence UASG. The negative control elements contribute to the broad range of inducibility of GAL1 and GAL10 by inhibiting two GAL4/galactose-independent activating elements (GAE1 and GAE2) in UASG. In turn, multiple GAL4-binding sites in UASG are necessary for GAL4 to overcome repression by the negative control elements under fully inducing conditions. When glucose in addition to galactose is available (repressing conditions), the ability of GAL4 to activate transcription is diminished as a result of its reduced affinity for DNA and the reduced availability of inducer. Under these conditions, the negative control elements inhibit transcriptional activation from the glucose-attenuated GAL4 sites, thus accounting at least in part for glucose repression acting in cis. A normal part of transcriptional regulation of the GAL1 and GAL10 genes, therefore, appears to involve a balance between the opposing functions of positive and negative control elements.

Differential repression of GAL4 and adjacent transcription activators by operators in the yeast GAL upstream activating sequence.

The upstream activating sequence of the adjacent and divergently transcribed GAL1 and GAL10 genes of Saccharomyces cerevisiae (UASG) contains at least three distinct classes of overlapping transcriptional control sites. The transcription activator GAL4 binds to four related sites in UASG and induces expression of GAL1 and GAL10 when galactose is available. We showed that UASG contains two additional positive control sites, designated GAL4/galactose-independent activating elements (GAEs), which reside at positions adjacent to or overlapping the GAL4-binding sites. When separated from neighboring sequences in UASG, the GAEs activate transcription independently of GAL4 with no requirement for galactose. In the intact GAL1-GAL10 divergent promoter region, their activity is ordinarily repressed by multiple negative control elements, the GAL operators. When galactose is available, GAL4 overcomes the activity of the GAL operators, while the putative GAE-binding proteins stay repressed. Combined, these results imply that distinct activators (GAL4 and GAE proteins) bound at adjacent or overlapping sites in UASG are differentially regulated by putative repressor proteins simultaneously bound at adjacent GAL operators. We surmise that GAE1 and GAE2 may have a physiological function other than regulation of galactose catabolism per se and discuss three hypotheses to account for their presence in UASG.

Button bolsters in dermatologic surgery.

Ordinary plastic buttons may be used as bolster devices to relieve tension across wounds. This article describes the method of placement of those "button bolsters" and suggests two methods of closing the wound once they are in place. This simple technique is easily mastered and gives additional wound closure security in the initial phase of wound healing.