RESUMO
The genome of Saccharomyces cerevisiae contains numerous unstable microsatellite sequences. Mononucleotide and dinucleotide repeats are rarely found in ORFs, and when present in an ORF are frequently located in an intron or at the C terminus of the protein, suggesting that their instability is deleterious to gene function. DNA trinucleotide repeats (TNRs) are found at a higher-than-expected frequency within ORFs, and the amino acids encoded by the TNRs represent a biased set. TNRs are rarely conserved between genes with related sequences, suggesting high instability or a recent origin. The genes in which TNRs are most frequently found are related to cellular regulation. The protein structural database is notably lacking in proteins containing amino acid tracts, suggesting that they are not located in structured regions of a protein but are rather located between domains. This conclusion is consistent with the location of amino acid tracts in two protein families. The preferred location of TNRs within the ORFs of genes related to cellular regulation together with their instability suggest that TNRs could have an important role in speciation. Specifically, TNRs could serve as hot spots for recombination leading to domain swapping, or mutation of TNRs could allow rapid evolution of new domains of protein structure.
Assuntos
Genes Fúngicos , Família Multigênica , Saccharomyces cerevisiae/genética , Repetições de Trinucleotídeos , Sequência de Aminoácidos , Aminoácidos , Sequência de Bases , DNA Fúngico , Repetições de Dinucleotídeos , Proteínas Fúngicas/genética , Genoma Fúngico , Repetições de Microssatélites , Dados de Sequência Molecular , Polimorfismo Genético , Sequências Reguladoras de Ácido NucleicoRESUMO
To determine when a glucose-repressed alcohol dehydrogenase isozyme and its regulatory gene, ADR1, arose during evolution, we surveyed species of the genus Saccharomyces for glucose-repressed ADH isozymes and for ADR1 homologues. Glucose-repressed ADH isozymes were present in all species of Saccharomyces sensu strictu and also in Saccharomyces kluyveri, the most distant member of the Saccharomyces clade. We cloned and characterized ADH promoters from S. bayanus, S. douglasii, and S. kluyveri. The ADH promoters from S. bayanus and S. douglasii had conserved sequences, including upstream regulatory elements, and an extended polydA tract. The expression of a reporter gene driven by the S. bayanus promoter was glucose-repressed and dependent on the major activator of transcription, ADR1, when it was introduced into S. cerevisiae. One S. kluyveri promoter was also glucose-repressed and ADR1-dependent in S. cerevisiae. The other S. kluyveri ADH promoter was expressed constitutively and was ADR1-independent. Although showing little sequence conservation with the S. cerevisiae ADH2 promoter, the glucose-repressed S. kluyveri promoter contains numerous potential binding sites for Adr1. The glucose-repressed ADH from S. kluyveri is a mitochondrial isozyme most closely related to S. cerevisiae ADHIII. ADR1 homologues from S. douglasii and S. paradoxus contain a trinucleotide repeat encoding polyAsn that is lacking in S. cerevisiae and S. bayanus. No ADR1 homologue could be detected in S. kluyveri, suggesting that the potential for Adr1 regulation may have arisen first, before ADR1 evolved.
Assuntos
Álcool Desidrogenase/genética , Evolução Molecular , Glucose/fisiologia , Proteínas de Saccharomyces cerevisiae , Saccharomyces/genética , Álcool Desidrogenase/metabolismo , Sequência de Bases , DNA Fúngico/química , DNA Fúngico/genética , DNA Fúngico/isolamento & purificação , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/fisiologia , Regulação Enzimológica da Expressão Gênica , Regulação Fúngica da Expressão Gênica , Isoenzimas/genética , Isoenzimas/metabolismo , Óperon Lac/genética , Mitocôndrias/enzimologia , Dados de Sequência Molecular , Mutagênese , Filogenia , Regiões Promotoras Genéticas/genética , Proteínas Recombinantes de Fusão/genética , Sequências Reguladoras de Ácido Nucleico , Saccharomyces/enzimologia , Saccharomyces cerevisiae/genética , Alinhamento de Sequência , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico , Fatores de Transcrição/genética , Fatores de Transcrição/fisiologiaRESUMO
The assessment of fetal dose from a special procedure in the clinical environment is difficult as patient size, fluoroscopic beam motion, and imaging sequences vary significantly from study to study. Fetal dose is particularly difficult to estimate when the fetus is exposed partially or totally to scatter radiation from images taken in other locations of the mother's body. A method to reliably estimate fetal dose has been developed by using template based input files for the Monte Carlo radiation transport code MCNP. Female patient phantoms at 0, 3, 6, and 9 months of pregnancy and source terms for common diagnostic tube potentials are used to rapidly build an input file for MCNP. The phantoms can be easily modified to fit patient shape. The geometry and beam location for each type of image acquired (i.e. fluoroscopy, spot filming, etc.) is verified by the use of a 3D visualization code (Sabrina). MCNP is then run to estimate the dose to the embryo/fetus and the exposure to skin entrance (ESE) for the beam being modeled. The actual ESE for the beam is then measured with ion chambers and the fetal dose is determined from the MCNP supplied ratio of ESE to fetal dose. Runs are made for each type of imaging and the doses are summed for the total fetal dose. For most procedures, the method can provide an estimate of the fetal dose within one day of the study. The method can also be used to prospectively model a study in order to choose imaging sequences that will minimize fetal dose.
Assuntos
Feto/efeitos da radiação , Fenômenos Biofísicos , Biofísica , Colangiopancreatografia Retrógrada Endoscópica , Feminino , Fluoroscopia , Humanos , Modelos Teóricos , Método de Monte Carlo , Gravidez , Doses de Radiação , UreteroscopiaRESUMO
Recent recommendations by the NCRP and the ICRP have lowered the nonoccupational dose limit from 5 mSv y-1 to 1 mSv y-1 [corrected]. This change has also been incorporated in the recently revised Title 10 Code of Federal Regulations, Part 20. Shielding installed in most current diagnostic x-ray rooms was based on the 5-mSv limit when rooms or corridors adjacent to the x-ray room were unrestricted areas. A computer model for evaluating shielding in a diagnostic x-ray room has been developed using the following: the Monte Carlo Code MCNP, all materials that would normally attenuate the beam in an x-ray room, realistic assumptions for work load, and a spectrum of tube potentials based on actual usage. Results indicate that most radiographic x-ray rooms with shielding designed using the conservative assumptions in NCRP 49 will meet the new standards.
