SEARCH · Search PubMed

Results for “MUTATION”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources

PubMed1993

Cystic fibrosis mutations in white and black Americans: an approach to identification of unknown mutations with implications for cystic fibrosis screening.

OBJECTIVE: We sought to define the frequency of common cystic fibrosis mutations in white and black American probands from our geographic region. STUDY DESIGN: Mutation analysis was performed for delta F508, G551D, G542X, R553X, S549N, an d N1303K. For probands with undetermined mutations single-stranded conformational polymorphism analysis was performed. RESULTS: Among 40 white subjects with cystic fibrosis 26 (65%) were homozygous for delta F508, 10 (25%) were heterozygous for delta F508 and another unknown mutation, and two were homozygous for unknown mutations. Among 10 black probands one was homozygous for delta F508, seven (70%) were heterozygous for delta F508 and another unknown mutation, and one was homozygous for unknown mutations. Single-stranded conformational polymorphism analysis for selected exons was performed for 11 probands with unknown mutations. One mutation was detected in a white proband. Sequencing of this exon showed the mutation to be Q493X. CONCLUSIONS: Thirty percent of white subjects and 80% of black subjects carried unknown mutations. In one family single-stranded conformational polymorphism was informative in identifying an undetermined cystic fibrosis mutation.

Black People↗

PubMed1982

The stability of mutator (MR)-induced X-chromosomal recessive visible mutations in Drosophila melanogaster.

In Drosophila, MR (male recombination) second chromosomes are known to act as mutators and recombination inducers in males. The induction of visible mutations by MR is observed at only a limited number of genes, such as singed bristle (sn), raspberry eye colour (ras), yellow body colour (y) and a carmine eye colour (car). Furthermore, sn mutations induced by MR are highly unstable, changing from a strong to a weak expression or reverting to the wild-type. It has been hypothesized by analogy with IS mutations in microorganisms, that MR-induced mutations also represent mutations of the insertion type. In this investigation the stability of two MR-h12-induced X-linked visible mutations was tested, one singed (snMR) and one raspberry (rasMR). The reversion frequency of both MR-induced mutations was low in the base population as well as upon outcrossing to C(1)DX, yw f females. The data reported here show that the MR-induced mutations become highly unstable when MR is re-introduced. The change of expression of an MR-induced mutation to a weaker phenotype or to the wild-type occurred at a frequency of 3.3 X 10(-3) (ras) to 20.4 X 10(-3) (sn). Recessive lethal mutations induced by MR in the X-chromosomes carrying the MR-induced singed or raspberry mutation were isolated and analysed. Among 11 independently MR-induced lethals in the rasMR-carrying X-chromosome, 4 were found to be allelic to a small deficiency that included the raspberry gene. 13 lethals were induced by MR in the snMR-carrying X-chromosome. Of these, 3 were located near the sn locus but none was allelic to a deficiency including the singed gene.

Animals↗

PubMed2005

MtDNA point mutations are associated with deletion mutations in aged rat.

The age-dependent accumulation of point mutations in the control region of human mtDNA has been suggested to contribute to aging processes. We investigated whether mtDNA point mutations accumulate to detectable levels in this region of mtDNA from aged Fischer 344 X Brown Norway F(1) hybrid rats. The control region and a portion of the major arc region (nucleotides 4386-7707) of the mtDNA were PCR-amplified and directly sequenced from microdissected single cardiomyocytes and single skeletal muscle fibers of 36-month old rats. Point mutations were not observed in these regions of the full-length mtDNA. Point mutations were, however, associated with deletion mutations, especially in cardiac cells. Approximately 40% of the deletion mutations identified in heart contained a point mutation, whereas only 1.9% of deletion mutations in skeletal muscle contained a point mutation. Point mutations were located adjacent to the deletion breakpoints and each point mutation was unique. In aged rats, point mutations are clonally expanded only when associated with deletion events suggesting that there are important differences between rats and humans in the mechanisms that cause mtDNA abnormalities.

Aging↗

PubMed2006

Mutations, mutation rates, and evolution at the hypervariable VNTR loci of Yersinia pestis.

VNTRs are able to discriminate among closely related isolates of recently emerged clonal pathogens, including Yersinia pestis the etiologic agent of plague, because of their great diversity. Diversity is driven largely by mutation but little is known about VNTR mutation rates, factors affecting mutation rates, or the mutational mechanisms. The molecular epidemiological utility of VNTRs will be greatly enhanced when this foundational knowledge is available. Here, we measure mutation rates for 43 VNTR loci in Y. pestis using an in vitro generated population encompassing approximately 96,000 generations. We estimate the combined 43-locus rate and individual rates for 14 loci. A comparison of Y. pestis and Escherichia coli O157:H7 VNTR mutation rates and products revealed a similar relationship between diversity and mutation rate in these two species. Likewise, the relationship between repeat copy number and mutation rate is nearly identical between these species, suggesting a generalized relationship that may be applicable to other species. The single- versus multiple-repeat mutation ratios and the insertion versus deletion mutation ratios were also similar, providing support for a general model for the mutations associated with VNTRs. Finally, we use two small sets of Y. pestis isolates to show how this general model and our estimated mutation rates can be used to compare alternate phylogenies, and to evaluate the significance of genotype matches, near-matches, and mismatches found in empirical comparisons with a reference database.

Animals↗

PubMed2002

Different patterns of bcl-6 and p53 gene mutations in tonsillar B cells indicate separate mutational mechanisms.

Mutations within the 5'-non-coding region of the bcl-6 gene can occur in lymphomas that originate from germinal centers (GCs), as well as in normal memory and GC B cells. Mutations in the p53 gene occur in 50% of human cancers. Since both bcl-6 and p53 can be mutated in certain circumstances, we investigated the accumulation of mutations in these genes in individual tonsillar B and T cells to determine whether the mutations exhibited a pattern anticipated from the B-cell hypermutation machinery. In tonsillar GC B cells, the overall mutational frequencies in the 5'-non-coding region of the bcl-6 gene was 0.85 x 10(-3)/bp. In contrast, there were no mutations in a region 2.8 kb downstream of the promoter. RGYW (purine, guanine, pyrimidine, A/T) targeting and a significantly lower mutational frequency in nai;ve B and GC founder B cells compared with GC B cells suggested that a similar mutator mechanism was active on Ig genes and this non-Ig gene. The mutational frequency in the exon-7-region of p53 was similar in the GC, memory and nai;ve B-cell subsets (1.02 x 10(-3) to 1.25 x 10(-3)/bp). RGYW/WRCY motifs were not targeted preferentially in the p53 gene. Moreover, a comparable mutational frequency of p53 was noted in tonsillar B and T cells. Hence, mutations in p53 do not appear to be the result of the B-cell hypermutational mechanism.

B-Lymphocytes↗

PubMed2001

Prothrombin 20210 G: a mutation and Factor V Leiden mutation in women with a history of severe preeclampsia and (H)ELLP syndrome.

OBJECTIVE: The 20210 G-A prothrombin gene variant and the Factor V Leiden mutation are mutations associated with venous thrombotic risk. The aim of our study was to assess the prevalence of these specific mutations in women with a history of preeclampsia or hemolysis elevated liver enzymes, and low platelet count [(H)ELLP] syndrome and their influence on perinatal outcome. In addition, the association with venous thromboembolism was assessed. METHODS: One hundred fourteen (114) women with a history of preeclampsia or (H)ELLP syndrome were investigated at least 3 months' postpartum for the presence of 20210 G-A prothrombin gene variant and Factor V Leiden mutation. RESULTS: Four (3.5%) of the women had the 20210 G-A prothrombin gene variant, four (3.5%) women had the Factor V Leiden mutation, and one of these women carried both mutations. The prevalence of prothrombin 20210 G-A prothrombin and Factor V Leiden mutation in women with severe preeclampsia or (H)ELLP syndrome were comparable with the prevalence in the general Dutch population. The odds ratio for thromboembolism for carriers versus noncarriers was 22 (95% confidence interval: 1.7-303). Perinatal mortality was not significantly higher in women with any mutation [odds ratio: 1.5 (0.2-9.5)]. CONCLUSIONS: Although our study confirms that prothrombin 20210 G-A mutation and Factor V Leiden mutation are important genetic risk factors associated with thrombotic risk, these mutations appear not related to perinatal outcome in women with preeclampsia or (H)ELLP syndrome. It is unlikely that these mutations are of major importance for the development of severe preeclampsia or (H)ELLP syndrome.

Adult↗

PubMed1992

Generation and analysis of random point mutations in an antibody CDR2 sequence: many mutated antibodies lose their ability to bind antigen.

We have investigated the impact of mutations on the binding functions of the phosphocholine (PC)-specific T15 antibody in the absence of antigen selection pressure. The H chain complementarity determining region 2 (CDR2) sequence of T15 antibody was saturated with point mutations by in vitro random mutagenesis. From the mutant library, 289 clones were screened by direct DNA sequencing. The point mutations generated by this method were randomly distributed throughout the CDR2 region and included all kinds of substitutions. 46 unique mutant antibodies, containing one to four point mutations each, were expressed in SP2/0 myeloma cells. Functional analysis on these antibodies has provided insights into several aspects of somatic mutation. (a) The majority (26/46) of mutant antibodies either lost (20/46) or had reduced (6/46) ability to bind PC-protein conjugates or R36a, a PC-expressing strain of Streptococcus pneumoniae. In contrast, none of the mutant antibodies displayed increased binding for these PC antigens. Taken together with calculations of destructive mutations elsewhere in the V region, the data suggest that somatic mutation may cause extensive wastage among B cells during clonal expansion after antigen stimulation. (b) The frequency of binding-loss mutants increased sharply when a second mutation was introduced into the CDR2 sequence; it appears that, in some cases, two or more mutations are needed to destroy binding. (c) The mutant antibodies were tested for their reactivity to 11 non-PC antigens as well as to three PC analogues. None of the mutants gained new reactivity or changed their ability to discriminate structural analogues, supporting the notion that the major role of somatic mutation is to increase or decrease affinity rather than to create new specificities. (d) Mutations in at least five different positions in CDR2 were deleterious, suggesting that these residues may be essential for antigen binding. Three of these positions are novel in that they had not been identified to be important for binding PC by previous crystallographic analysis. (e) Introduction of mutations into two highly conserved residues in CDR2 did not alter the overall conformation of the V region as judged by antiidiotypic analysis, and, in some cases, did not affect the antigen binding function. The results thus indicate that even nonconservative substitutions of invariant residues need not be deleterious, suggesting that their conservation may be due to reasons other than maintaining antibody structure or specificity.

Amino Acid Sequence↗

PubMed1998

Identification of constitutional WT1 mutations, in patients with isolated diffuse mesangial sclerosis, and analysis of genotype/phenotype correlations by use of a computerized mutation database.

Constitutional mutations of the WT1 gene, encoding a zinc-finger transcription factor involved in renal and gonadal development, are found in most patients with Denys-Drash syndrome (DDS), or diffuse mesangial sclerosis (DMS) associated with pseudohermaphroditism and/or Wilms tumor (WT). Most mutations in DDS patients lie in exon 8 or exon 9, encoding zinc finger 2 or zinc finger 3, respectively, with a hot spot (R394W) in exon 9. We analyzed a series of 24 patients, 10 with isolated DMS (IDMS), 10 with DDS, and 4 with urogenital abnormalities and/or WT. We report WT1 heterozygous mutations in 16 patients, 4 of whom presented with IDMS. One male and two female IDMS patients with WT1 mutations underwent normal puberty. Two mutations associated with IDMS are different from those described in DDS patients. No WT1 mutations were detected in the six other IDMS patients, suggesting genetic heterogeneity of this disease. We analyzed genotype/phenotype correlations, on the basis of the constitution of a WT1 mutation database of 84 germ-line mutations, to compare the distribution and type of mutations, according to the different symptoms. This demonstrated (1) the association between mutations in exons 8 and 9 and DMS; (2) among patients with DMS, a higher frequency of exon 8 mutations among 46, XY patients with female phenotype than among 46,XY patients with sexual ambiguity or male phenotype; and (3) statistically significant evidence that mutations in exons 8 and 9 preferentially affect amino acids with different functions.

Amino Acid Sequence↗

PubMed1998

Functional characterization of missense mutations in ATP7B: Wilson disease mutation or normal variant?

Wilson disease is an autosomal recessive disorder of copper transport that causes hepatic and/or neurological disease resulting from copper accumulation in the liver and brain. The protein defective in this disorder is a putative copper-transporting P-type ATPase, ATP7B. More than 100 mutations have been identified in the ATP7B gene of patients with Wilson disease. To determine the effect of Wilson disease missense mutations on ATP7B function, we have developed a yeast complementation assay based on the ability of ATP7B to complement the high-affinity iron-uptake deficiency of the yeast mutant ccc2. We characterized missense mutations found in the predicted membrane-spanning segments of ATP7B. Ten mutations have been made in the ATP7B cDNA by site-directed mutagenesis: five Wilson disease missense mutations, two mutations originally classified as possible disease-causing mutations, two putative ATP7B normal variants, and mutation of the cysteine-proline-cysteine (CPC) motif conserved in heavy-metal-transporting P-type ATPases. All seven putative Wilson disease mutants tested were able to at least partially complement ccc2 mutant yeast, indicating that they retain some ability to transport copper. One mutation was a temperature-sensitive mutation that was able to complement ccc2 mutant yeast at 30 degreesC but was unable to complement at 37 degreesC. Mutation of the CPC motif resulted in a nonfunctional protein, which demonstrates that this motif is essential for copper transport by ATP7B. Of the two putative ATP7B normal variants tested, one resulted in a nonfunctional protein, which suggests that it is a disease-causing mutation.

Adenosine Triphosphatases↗

PubMed2005

Comparison of amplification refractory mutation system and polymerase chain reaction-restriction fragment length polymorphism techniques used for the investigation of MEFV gene exon 10 point mutations in familial Mediterranean fever patients living in Cukurova region (Turkey).

Familial Mediterranean fever (FMF) is an autosomal recessive inherited disease characterized by recurrent fever, serositis and arthritis. The disease is highly prevalent in Mediterranean basin populations. Recently, the gene responsible for FMF (MEFV) was cloned and at least 40 MEFV gene mutations have been identified. The most frequently observed mutations in the MEFV gene are M694V, M694I, M680I, and V726A. These occur within exon 10 of the gene, and account for 85% of the known MEFV alleles. In this study, the reliability and economical aspects of amplification refractory mutation system (ARMS) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) techniques were compared for analyzing the frequencies of the major point mutations of 90 unrelated patients with FMF from the Cukurova region in Turkey. Both techniques yielded similar results: The ratio of independent alleles of 90 patients carrying one of the tested mutations was 81.1%; patients consisted of 12 different genotypes. In 64 of 90 patients (71.1%) mutations were observed in both alleles. Thirty-six patients (40%) were homozygous for the same mutation, 28 (31.1%) were heterozygous for different mutations. Eighteen patients (20%) were heterozygous for one allele with one of the four mutations but the other allele was unknown. In 8 patients (8.8%) no mutation could be detected. The most frequently observed mutation was M694V (51.66%), followed by M680I (17.22%), V726A (10.55%), and M694I (1.66%). In conclusion ARMS and PCR-RFLP techniques were equally reliable to detect the mutations in Turkish FMF patients. However, the ARMS technique was found to be more rapid and economical than the PCR-RFLP techniques.

Exons↗

PubMed2000

Properties of ethylmethane sulfonate-induced mutations affecting life-history traits in Caenorhabditis elegans and inferences about bivariate distributions of mutation effects.

The homozygous effects of ethylmethane sulfonate (EMS)-induced mutations in Caenorhabditis elegans are compared across life-history traits. Mutagenesis has a greater effect on early than late reproductive output, since EMS-induced mutations tend to cause delayed reproduction. Mutagenesis changes the mean and variance of longevity much less than reproductive output traits. Mutations that increase total or early productivity are not detected, but the net effect of mutations is to increase and decrease late productivity to approximately equal extents. Although most mutations decrease longevity, a mutant line with increased longevity was found. A flattening of mortality curves with age is noted, particularly in EMS lines. We infer that less than one-tenth of mutations that have fitness effects in natural conditions are detected in the laboratory, and such mutations have moderately large effects ( approximately 20% of the mean). Mutational correlations for life-history traits are strong and positive. Correlations between early or late productivity and longevity are of similar magnitude. We develop a maximum-likelihood procedure to infer bivariate distributions of mutation effects. We show that strong mutation-induced genetic correlations do not necessarily imply strong directional correlations between mutational effects, since correlation is also generated by lines carrying different numbers of mutations.

Animals↗

PubMed2000

Somatic mutation screening: identification of individuals harboring K-ras mutations with the use of plasma DNA.

BACKGROUND: Many cancers are attributed to somatic mutation of DNA. We investigated whether it is feasible to detect cancer-associated somatic mutations in patients with neoplasms by using plasma DNA. METHODS: Plasma samples were prospectively collected from 240 patients undergoing colonoscopy. Colorectal biopsies were performed as clinically indicated in 135 patients, and risk factor information was available from 232 patients. DNA was extracted from plasma and colorectal tissue and was amplified by use of a polymerase chain reaction method that enriches for mutations in codon 12 of the K-ras oncogene. Molecular, histologic, and clinical data were compared by use of two-sided Fisher's exact test. RESULTS: Mutations in the K-ras gene detected in the plasma of 64 (28%) of 232 patients were statistically significantly associated with colorectal cancer risk factors (P =.0002). Of those patients having tissue available for comparison (n = 135), mutations in the K-ras gene were found in the tissues of 35 patients, and 29 (83%) of these 35 showed mutations in plasma samples. In contrast, the plasma assay was negative in 93 of the 100 patients whose tissue K-ras was wild-type. Among patients without biopsies (n = 105), 28 had mutated K-ras in their plasma DNA, despite the absence of remarkable colonoscopy findings; 24 of these 28 patients had risk factors for colorectal cancer. Overall, 25 (39%) of 64 patients showing mutations in plasma DNA had colorectal neoplasms with K-ras mutations compared with five (3%) of 176 patients without K-ras mutations in plasma DNA. CONCLUSION: Plasma DNA assays for the detection of mutations in K-ras codon 12 may provide a feasible method to screen populations for somatic mutations frequently found in neoplasms. The clinical utility of using this test in screening populations requires further study.

Adenoma↗

PubMedDate not supplied

Identification of novel mutations and the three most common mutations in the human ATP7B gene of Korean patients with Wilson disease.

PURPOSE: Wilson disease, an autosomal recessive disorder of copper transport, is probably the most common inherited metabolic disorder in Korea. In Wilson disease, synthesis of a defective copper transporting enzyme leads to the accumulation of copper in the liver, brain, and kidney. The product of the Wilson disease gene is a copper transporting P-type ATPase (ATP7B). In this study, efforts were made to identify novel mutations and investigate the frequency of the common mutations in Korean patients with Wilson disease. METHODS: This study includes 37 patients from 33 unrelated Korean families with Wilson disease. Genomic DNA from peripheral leukocytes or skin fibroblasts and cDNA from liver tissue were polymerase chain reaction-amplified exon by exon and subsequently analyzed using heteroduplex or single-strand conformation polymorphism analysis. Specimens showing mobility shift on those studies were directly sequenced. RESULTS: Twelve different mutations in 33 Korean families with Wilson disease were identified: Arg778Leu (R778L), Asn1270Ser (N1270S), Ala874Val (A874V), 2303-2305delC, 2630-2656del, 2460-2462insC, Cys656Stop (C656X), Pro768His (P768H), Leu1083Phe (L1083F), Ala1168Ser (A1168S), Leu1255Ile (L1255I), and Asp1267Ala (D1267A). Among these, six mutations (2630-2656del, 2460-2462insC, C656X, P768H, A1168S, and L1255I) are novel. The R778L mutation is known to be highly prevalent in Asian patients. The allele frequency of R778L in Korean patients with Wilson disease was 37.9%, which was significantly higher than those of Japanese and Taiwanese patients. The N1270S mutation, originally described in an Italian patient, was the next most common mutation in Korean patients, with an allele frequency of 12.1%, which was presumed to disrupt the ATP hinge domain of the ATP7B protein. The A874V mutation was the third most common mutation with an allele frequency of 9.4%, which was presumed to disrupt the Td domain of the ATP7B protein. CONCLUSION: The R778L, N1270S, and A874V mutations are three major mutations representing approximately 60% of mutated alleles, although Korean patients with Wilson disease are genetically heterogeneous.

Adenosine Triphosphatases↗

PubMed2006

EGFR point mutation in non-small cell lung cancer is occasionally accompanied by a second mutation or amplification.

Activating mutations of EGFR are found frequently in a subgroup of patients with non-small cell lung cancer (NSCLC) and are highly correlated with the response to gefitinib and erlotinib. In the present study, we searched for mutations of EGFR, HER2 and KRAS in 264 resected primary NSCLC from Japanese patients and determined whether there is a correlation between genetic alterations of these genes and clinicopathological factors, together with 85 tumors that we reported previously. EGFR mutations were found in 102 of the total 349 tumors, and seven tumors had two missense mutations. Reverse transcription-polymerase chain reaction of EGFR and subsequent subcloning analyses identified that the double mutations occurred in the same allele. Furthermore, in 202 NSCLC analyzed by Southern blotting, we identified 11 tumors with gene amplification of EGFR, with eight tumors containing a mutation in EGFR. Sequence analysis detected only weak or no signals of the wild-type allele in the eight tumors, strongly suggesting that the mutated allele was amplified selectively. These findings indicate that a dual genetic change of EGFR can occur in the same allele either with a possible second-hit mutation or with amplification, which may imply a more selective growth advantage in a cancer cell. Meanwhile, HER2 mutations and amplifications were found in six of 349 tumors and three of 202 tumors, respectively, and KRAS mutations in 21 of 349 tumors. Mutations of the EGFR and HER2 genes were more frequently found in female never or light-smoking patients with adenocarcinoma, and there were no tumors that had two or more mutations simultaneously among EGFR, HER2 and KRAS. The current study further demonstrates that a double genetic event in EGFR can occasionally occur in lung cancer, thus providing new clues for understanding the involvement of epidermal growth factor receptor signaling cascades in the pathogenesis of NSCLC.

Adult↗

PubMed1993

Occurrence of point mutations in p53 gene is not increased in patients with acute myeloid leukaemia carrying an activating N-ras mutation.

The frequency of simultaneously detecting N-ras and p53 gene mutations was studied in leukaemia cells of patients with acute myeloid leukaemia (AML) or with myelodysplastic syndrome (MDS). Using in vitro DNA amplification followed by oligonucleotide hybridization analysis, 45 AML and six MDS patients were screened for activating mutations in codons 12, 13 and 61 of N-ras. Ten of them (eight AML and two MDS) were found positive. These 10 patients and 10 others without activating N-ras mutation were further analysed by direct sequencing of the amplified exons for p53 mutations and for atypical N-ras mutations. Beside the activating mutations in the N-ras gene, no additional transforming or nontransforming mutations could be detected in the N-ras. However, exon 7 of p53 was mutated in two AML patients without activating N-ras mutation. These data show that p53 mutations occurred with half the frequency of N-ras mutations in AML and that no positive correlation could be found between the onset of mutations in N-ras and p53 genes.

Acute Disease↗

PubMed2003

Correlation of phenotypic zidovudine resistance with mutational patterns in the reverse transcriptase of human immunodeficiency virus type 1: interpretation of established mutations and characterization of new polymorphisms at codons 208, 211, and 214.

Zidovudine resistance (ZDV-R) is associated with classic genotypic changes at codons 41, 67, 70, 210, 215, and 219 of the human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) gene as well as with the multinucleoside resistance (MNR) complexes (Q151M MNR complex; 6-bp insertion/A62V complex). In addition, enhanced resistance to ZDV in the context of the classic ZDV mutations plus the M184V mutation has been associated with additional mutations at positions 208, 211, 214, and 333. In this study we investigated phenotypic ZDV-R determined by a recombinant virus assay (Antivirogram; Virco) in 223 clinical samples in relation to the above genotypic changes. 150 out of 223 clinical samples had the M184V mutation. Phenotypic ZDV-R ranged from 0.3- to 5,338-fold. Sixteen samples (15 with high ZDV-R ranging from 90- to 3,571-fold) contained MNR-associated patterns. Analysis of classic mutational patterns broadly demonstrated increasing ZDV-R with increasing number of ZDV mutations. A comparable correlation was obtained when ZDV-R was analyzed only relative to the T215Y/F mutation. Site-directed mutagenesis experiments investigating the influence of the additional mutations H208Y, R211K, and L214F on ZDV-R resulted in a 7.4- or 21-fold increase in ZDV-R when the R211K/L214F or H208Y/R211K/L214F mutations, respectively, were added to a highly ZDV-R virus. In the clinical sample data set we analyzed, the combination of R211K/L214F appeared most frequently. The H208Y change was detected only in highly ZDV-R viruses, whereas the G333E/D change was distributed equally. All changes were independent of the M184V mutation. A 2.4- or 8-fold increase in ZDV-R was observed in the clinical samples with high ZDV-R containing the R211K/L214F or H208Y/R211K/L214F mutations, respectively. We have shown that the combination of the additional mutations H208Y, R211K, and L214F in HIV-1 RT may influence ZDV-R and should be considered when assessing ZDV-R.

Base Sequence↗

PubMed2002

Regulation of mutY and nature of mutator mutations in Escherichia coli populations under nutrient limitation.

Previous analysis of aerobic, glucose-limited continuous cultures of Escherichia coli revealed that G:C-to-T:A (G:C-->T:A) transversions were the most commonly occurring type of spontaneous mutation. One possible explanation for the preponderance of these mutations was that nutrient limitation repressed MutY-dependent DNA repair, resulting in increased proportions of G:C-->T:A transversions. The regulation of the mutY-dependent DNA repair system was therefore studied with a transcriptional mutY-lacZ fusion recombined into the chromosome. Expression from the mutY promoter was fourfold higher under aerobic conditions than under anaerobic conditions. But mutY expression was higher in glucose- or ammonia-limited chemostats than in nutrient-excess batch culture, so mutY was not downregulated by nutrient limitation. An alternative explanation for the frequency of G:C-->T:A transversions was the common appearance of mutY mutator mutations in the chemostat populations. Of 11 chemostat populations screened in detail, six contained mutators, and the mutator mutation in four cultures was located in the region of mutY at 66 min on the chromosome. The spectrum of mutations and rate of mutation in these isolates were fully consistent with a mutY-deficiency in each strain. Based on PCR analysis of the region within and around mutY, isolates from three individual populations contained deletions extending at least 2 kb upstream of mutY and more than 5 kb downstream. In the fourth population, the deletion was even longer, extending at least 5 kb upstream and 5 kb downstream of mutY. The isolation of mutY mutator strains from four independent populations with extensive chromosomal rearrangements suggests that mutY inactivation by deletion is a means of increasing mutation rates under nutrient limitation and explains the observed frequency of G:C-->T:A mutations in glucose-limited chemostats.

DNA Glycosylases↗

PubMed1999

Mutator phenotypes conferred by MLH1 overexpression and by heterozygosity for mlh1 mutations.

Loss of DNA mismatch repair due to mutation or diminished expression of the MLH1 gene is associated with genome instability and cancer. In this study, we used a yeast model system to examine three circumstances relevant to modulation of MLH1 function. First, overexpression of wild-type MLH1 was found to cause a strong elevation of mutation rates at three different loci, similar to the mutator effect of MLH1 gene inactivation. Second, haploid yeast strains with any of six mlh1 missense mutations that mimic germ line mutations found in human cancer patients displayed a strong mutator phenotype consistent with loss of mismatch repair function. Five of these mutations affect amino acids that are homologous to residues suggested by recent crystal structure and biochemical analysis of Escherichia coli MutL to participate in ATP binding and hydrolysis. Finally, using a highly sensitive reporter gene, we detected a mutator phenotype of diploid yeast strains that are heterozygous for mlh1 mutations. Evidence suggesting that this mutator effect results not from reduced mismatch repair in the MLH1/mlh1 cells but rather from loss of the wild-type MLH1 allele in a fraction of cells is presented. Exposure to bleomycin or to UV irradiation strongly enhanced mutagenesis in the heterozygous strain but had little effect on the mutation rate in the wild-type strain. This damage-induced hypermutability may be relevant to cancer in humans with germ line mutations in only one MLH1 allele.

Adaptor Proteins, Signal Transducing↗