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Results for “Mutation Rate”

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PubMed2002

Environmental regulation of mutation rates at specific sites.

Recent studies on bacterial adaptation to stress suggest that bacteria can regulate the generation of mutations at specific sites in response to environmental conditions. Here, we review these findings and discuss the circumstances under which these mechanisms might prove advantageous.

Bacteria↗
PubMed1995

Spontaneous mutation rate of modifiers of metabolism in Drosophila.

A rigorous test of our understanding of evolutionary quantitative genetics would be to predict accurately the equilibrium distribution of a character from empirical estimates of the relevant parameters in a mutation-selection-drift balance model. An aspect of this problem that is amenable to experimental analysis is the distribution of the effects of new mutations. This study quantifies the divergence among 200 lines of Drosophila melanogaster as they accumulated mutations on the second chromosome and estimates the rate of increase of variation and covariation in metabolic characters. Amounts of stored triacylglycerol and glycogen and the activities of a series of 12 metabolic enzymes were assayed in a subset of lines at generations 0, 11, 22, 33 and 44. Analyses of the rate of increase in the among-line variance in each trait allowed estimation of Vm/Ve, the ratio of among-line variance added per generation to the environmental variance. Values of Vm/Ve for the second chromosome ranged from 0.0004 to 0.0289 per generation. Six of the 16 characters showed significant departure from a normal distribution, and several lines exhibited large changes in more than one character. The covariance of pairs of traits also was partitioned into a within-line component (environmental covariance, Cov(e)) and an among-line component (mutational covariance, Covm). Both variances and covariance among lines increased over time, as assessed by linear regression, whereas environmental covariance showed no such trend. Results indicate that the quantitative genetic parameters describing the variation in metabolic traits are similar to those of other continuous characters.

Analysis of Variance↗
PubMed2004

Mutations in Haemophilus influenzae mismatch repair genes increase mutation rates of dinucleotide repeat tracts but not dinucleotide repeat-driven pilin phase variation rates.

High-frequency, reversible switches in expression of surface antigens, referred to as phase variation (PV), are characteristic of Haemophilus influenzae. PV enables this bacterial species, an obligate commensal and pathogen of the human upper respiratory tract, to adapt to changes in the host environment. Phase-variable hemagglutinating pili are expressed by many H. influenzae isolates. PV involves alterations in the number of 5' TA repeats located between the -10 and -35 promoter elements of the overlapping, divergently orientated promoters of hifA and hifBCDE, whose products mediate biosynthesis and assembly of pili. Dinucleotide repeat tracts are destabilized by mismatch repair (MMR) mutations in Escherichia coli. The influence of mutations in MMR genes of H. influenzae strain Rd on dinucleotide repeat-mediated PV rates was investigated by using reporter constructs containing 20 5' AT repeats. Mutations in mutS, mutL, and mutH elevated rates approximately 30-fold, while rates in dam and uvrD mutants were increased 14- and 3-fold, respectively. PV rates of constructs containing 10 to 12 5' AT repeats were significantly elevated in mutS mutants of H. influenzae strains Rd and Eagan. An intact hif locus was found in 14 and 12% of representative nontypeable H. influenzae isolates associated with either otitis media or carriage, respectively. Nine or more tandem 5' TA repeats were present in the promoter region. Surprisingly, inactivation of mutS in two serotype b H. influenzae strains did not alter pilin PV rates. Thus, although functionally analogous to the E. coli MMR pathway and active on dinucleotide repeat tracts, defects in H. influenzae MMR do not affect 5' TA-mediated pilin PV.

5' Flanking Region↗
PubMed2000

The p53 gene in patients under the age of 40 with gastric cancer: mutation rates are low but are associated with a cardiac location.

BACKGROUND: Determining both the frequency and the spectrum of p53 gene mutation in young patients with gastric cancer might provide clues to the host related genetic mechanism(s) in gastric carcinogenesis. PATIENTS AND METHODS: p53 mutations were assessed (by means of polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), followed by DNA sequencing) in a cohort of 105 consecutive Italian patients in whom gastric cancer was ascertained before the age of 41. RESULTS: A low prevalence of p53 mutations (eight of 105) was observed, with no significant difference between intestinal (three of 31; 10%) and diffuse (five of 74; 7%) phenotypes. A significantly higher prevalence of p53 mutations was associated with the cardiac location (odds ratio, 7.09; confidence interval, 1.56 to 32.11). In all but one case, p53 mutations were associated with a stage higher than I. All eight mutations were located at CpG sites, where G : C to A : T transitions have been associated with frequent methylation at the C5 position of cytosine. CONCLUSIONS: These findings show that, unlike what has been consistently demonstrated in the general population, p53 mutations are uncommon in gastric cancer occurring in young patients, and in such patients, p53 alterations are significantly associated with the cardiac location.

Adolescent↗
PubMed1992

Mutation rates.

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Biological Evolution↗