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PubMed1994

Dominant negative mutator mutations in the mutS gene of Escherichia coli.

The MutS protein of Escherichia coli is part of the dam-directed MutHLS mismatch repair pathway which rectifies replication errors and which prevents recombination between related sequences. In order to more fully understand the role of MutS in these processes, dominant negative mutS mutations on a multicopy plasmid were isolated by screening transformed wild-type cells for a mutator phenotype, using a Lac+ papillation assay. Thirty-eight hydroxylamine- and 22 N-methyl-N'-nitro-N-nitrosoguanidine-induced dominant mutations were isolated. Nine of these mutations altered the P-loop motif of the ATP-binding site, resulting in four amino acid substitutions. With one exception, the remaining sequenced mutations all caused substitution of amino acids conserved during evolution. The dominant mutations in the P-loop consensus caused severely reduced repair of heteroduplex DNA in vivo in a mutS mutant host strain. In a wild-type strain, the level of repair was decreased by the dominant mutations to between 12 to 90% of the control value, which is consistent with interference of wild-type MutS function by the mutant proteins. Increasing the wild-type mutS gene dosage resulted in a reversal of the mutator phenotype in about 60% of the mutant strains, indicating that the mutant and wild-type proteins compete. In addition, 20 mutant isolates showed phenotypic reversal by increasing the gene copies of either mutL or mutH. There was a direct correlation between the levels of recombination and mutagenesis in the mutant strains, suggesting that these phenotypes are due to the same function of MutS.

Adenosine Triphosphatases↗
PubMed1997

Nonadaptive mutations occur on the F' episome during adaptive mutation conditions in Escherichia coli.

One of the most studied examples of adaptive mutation is a strain of Escherichia coli, FC40, that cannot utilize lactose (Lac-) but that readily reverts to lactose utilization (Lac+) when lactose is its sole carbon source. Adaptive reversion to Lac+ occurs at a high rate when the Lac- allele is on an F' episome and conjugal functions are expressed. It was previously shown that nonselected mutations on the chromosome did not appear in the Lac- population while episomal Lac+ mutations accumulated, but it remained possible that nonselected mutations might occur on the episome. To investigate this possibility, a second mutational target was created on the Lac- episome by mutation of a Tn1O element, which encodes tetracycline resistance (Tetr), to tetracycline sensitivity (Tets). Reversion rates to Tetr during normal growth and during lactose selection were measured. The results show that nonselected Tetr mutations do accumulate in Lac- cells when those cells are under selection to become Lac+. Thus, reversion to Lac+ in FC40 does not appear to be adaptive in the narrow sense of the word. In addition, the results suggest that during lactose selection, both Lac+ and Tetr mutations are created or preserved by the same recombination-dependent mechanism.

Adaptation, Physiological↗
PubMed1998

Compensatory point mutations in the human immunodeficiency virus type 1 Gag region that are distal from deletion mutations in the dimerization initiation site can restore viral replication.

The dimerization initiation site (DIS), downstream of the long terminal repeat within the human immunodeficiency virus type 1 (HIV-1) genome, can form a stem-loop structure (SL1) that has been shown to be involved in the packaging of viral RNA. In order to further determine the role of this region in the virus life cycle, we deleted the 16 nucleotides (nt) at positions +238 to +253 within SL1 to generate a construct termed BH10-LD3 and showed that this virus was impaired in viral RNA packaging, viral gene expression, and viral replication. Long-term culture of these mutated viruses in MT-2 cells, i.e., 18 passages, yielded revertant viruses that possessed infectivities similar to that of the wild type. Cloning and sequencing showed that these viruses retained the original 16-nt deletion but possessed two additional point mutations, which were located within the p2 and NC regions of the Gag coding region, respectively, and which were therefore named MP2 and MNC. Site-directed mutagenesis studies revealed that both of these point mutations were necessary to compensate for the 16-nt deletion in BH10-LD3. A construct with both the 16-nt deletion and the MP2 mutation, i.e., LD3-MP2, produced approximately five times more viral protein than BH10-LD3, while the MNC mutation, i.e., construct LD3-MNC, reversed the defects in viral RNA packaging. We also deleted nt +261 to +274 within the 3' end of SL1 and showed that the diminished infectivity of the mutated virus, termed BH10-LD4, could also be restored by the MP2 and MNC point mutations. Therefore, compensatory mutations within the p2 and NC proteins, distal from deletions within the DIS region of the HIV genome, can restore HIV replication, viral gene expression, and viral RNA packaging to control levels.

Amino Acid Sequence↗
PubMed1971

Specific suppression of mutations in genes 46 and 47 by das, a new class of mutations in bacteriophage T4D.

Mutants in T4 genes 46 and 47 exhibit early cessation of deoxyribonucleic acid (DNA) synthesis ("DNA arrest") and decreased synthesis of late proteins and phage. In addition, mutants in genes 46 and 47 fail to degrade host DNA to acidsoluble products. It is shown here that this complex phenotype can be partially suppressed by mutation of a T4 gene external to genes 46 and 47 which has been named das for "DNA arrest suppressor." The das mutations were discovered as third-site mutations in spontaneous pseudorevertants of [46, 47] mutants; the pseudorevertants make small plaques on Escherichia coli B, whereas [46, 47] mutants make none. The [das, 46, 47] triple mutant exhibits increased DNA, late protein, and viable phage production compared to the double mutant [46, 47]. The [das, 46, 47] mutant also degrades more of the host DNA to acid-soluble products than does the [46, 47] mutant. The suppressor effect of the das mutation appears to be gene-specific: it suppresses both amber and temperature-sensitive mutations in genes 46 and 47 and does not suppress amber mutations in any of the other genes tested. The [das] single mutants make normal-sized plaques on E. coli B and exhibit nearly normal host DNA degradation, DNA synthesis, late protein synthesis, and viable phage production. The das mutations either define a new gene between genes 33 and 34 or are special mutations within gene 33.

Carbon Isotopes↗
PubMed2005

A novel BRCA2 mutation in an Indonesian family found with a new, rapid, and sensitive mutation detection method based on pooled denaturing gradient gel electrophoresis and targeted sequencing.

BACKGROUND: Breast cancer is increasing in Indonesia and other developing countries. Germline mutations in the BRCA1/2 genes are most strongly associated with a high risk for breast cancer development. There have been no reports on BRCA1/2 gene mutations in the Indonesian population. Genetic research yielding insight into mutations affecting the Indonesian population can help in risk assessment of individual patients. AIMS: To screen the BRCA1/2 genes for mutations in early onset Indonesian breast cancer patients and their families with a new, simple, and sensitive BRCA1/2 mutation screening strategy based on denaturing gradient gel electrophoresis (DGGE) and targeted sequencing. METHODS: DNA was isolated from the blood of four Indonesian breast cancer patients from high risk families and seven family members, and the polymerase chain reaction was performed with specially designed primers throughout the BRCA1/2 coding sequences to produce fragments suitable for pooled DGGE analysis. The aberrantly migrating samples were reamplified and sequenced. RESULTS: Two mutations were found in exons 13 and 16 of BRCA1 and two mutations in exons 2 and 14 of BRCA2, which turned out to be established polymorphisms according to the Breast Cancer Information Core. In addition, a novel 6 bp deletion in exon 11, leading to a premature stop, was found in BRCA2. CONCLUSION: Pooled DGGE and targeted sequencing revealed four BRCA1/2 polymorphisms and one novel BRCA2 mutation in a group of Indonesian patients at high risk of hereditary breast cancer. This illustrates that the proposed method is sensitive and particularly suited for screening unknown populations.

Adult↗
PubMed2005

Mutation screening in Borjeson-Forssman-Lehmann syndrome: identification of a novel de novo PHF6 mutation in a female patient.

BACKGROUND: Börjeson-Forssman-Lehmann syndrome (BFLS; MIM 301900) is an infrequently described X linked disorder caused by mutations in PHF6, a novel zinc finger gene of unknown function. OBJECTIVE: To present the results of mutation screening in individuals referred for PHF6 testing and discuss the value of prior X-inactivation testing in the mothers of these individuals. RESULTS: 25 unrelated individuals were screened (24 male, one female). Five PHF6 mutations were detected, two of which (c.940A-->G and c.27_28insA) were novel. One of these new mutations, c.27_28insA, was identified in a female BFLS patient. This was shown to be a de novo mutation arising on the paternal chromosome. This is the first report of a clinically diagnosed BFLS female with a confirmed PHF6 mutation. In addition, the X-inactivation status of the mothers of 19 males with suggested clinical diagnosis of BFLS was determined. Skewed (> or =70%) X-inactivation was present in five mothers, three of whom had sons in whom a PHF6 mutation was detected. The mutation positive female also showed skewing. CONCLUSIONS: The results indicate that the success of PHF6 screening in males suspected of having BFLS is markedly increased if there is a positive family history and/or skewed X-inactivation is found in the mother.

Abnormalities, Multiple↗
PubMed2005

Cancer risks in first degree relatives of BRCA1 mutation carriers: effects of mutation and proband disease status.

BACKGROUND: Mutations in the BRCA1 (MIM 113705) gene are found in many families with multiple cases of breast and ovarian cancer, and women with a BRCA1 mutation are at significantly higher risk of developing breast and ovarian cancer than are the general public. METHODS: We obtained blood samples and pedigree information from 3568 unselected cases of early-onset breast cancer and 609 unselected patients with ovarian cancer from hospitals throughout Poland. Genetic testing was performed for three founder BRCA1 mutations. We also calculated the risk of breast and ovarian cancer to age 75 in the first degree relatives of carriers using Kaplan-Meier methods. RESULTS: The three founder BRCA1 mutations were identified in 273 samples (187 with 5382insC, 22 with 4153delA, and 64 with C61G). A mutation was present in 4.3% of patients with breast cancer and 12.3% of patients with ovarian cancer. The overall risk of breast cancer to age 75 in relatives was 33% and the risk of ovarian cancer was 15%. The risk for breast cancer was 42% higher among first degree relatives of carriers of the C61G missense mutation compared to other mutations (HR = 1.42; p = 0.10) and the risk for ovarian cancer was lower than average (OR = 0.26; p = 0.03). Relatives of women diagnosed with breast cancer had a higher risk of breast cancer than relatives of women diagnosed with ovarian cancer (OR = 1.7; p = 0.03). CONCLUSIONS: The risk of breast cancer in female relatives of women with a BRCA1 mutation depends on whether the proband was diagnosed with breast or ovarian cancer.

Adult↗
PubMed2006

Meta-analysis of the p53 mutation database for mutant p53 biological activity reveals a methodologic bias in mutation detection.

PURPOSE: Analyses of the pattern of p53 mutations have been essential for epidemiologic studies linking carcinogen exposure and cancer. We were concerned by the inclusion of dubious reports in the p53 databases that could lead to controversial analysis prejudicial to the scientific community. EXPERIMENTAL DESIGN: We used the universal mutation database p53 database (21,717 mutations) combined with a new p53 mutant activity database (2,300 mutants) to perform functional analysis of 1,992 publications reporting p53 alterations. This analysis was done using a statistical approach similar to that of clinical meta-analyses. RESULTS: This analysis reveals that some reports of infrequent mutations are associated with almost normal activities of p53 proteins. These particular mutations are frequently found in studies reporting multiple mutations in one tumor, silent mutations, or lacking mutation hotspots. These reports are often associated with particular methodologies, such as nested PCR, for which key controls are not satisfactory. CONCLUSIONS: We show the importance of accurate functional analysis before inferring any genetic variation. The quality of the p53 databases is essential in order to prevent erroneous analysis and/or conclusions. The availability of functional data from our new p53 web site (http://p53.free.fr and http://www.umd.be:2072/) will allow functional prescreening to identify potential artifactual data.

Databases, Factual↗
PubMed2005

The influence of premeiotic clusters of mutation on indirect estimations of mutation rate.

Based on the hypothesis that rare alleles are in mutation and random loss equilibrium, mutation rate can be indirectly estimated by measuring the number of rare variants and the average existing time of a mutant allele. This method can be applied to estimate the mutation rate in humans. However, this estimation of mutation rate is affected by the presence of premeiotic clusters of mutation. Mutation clusters change both the number of initial mutants and the average existing time of a mutant allele. As a result, the formula indirectly estimating mutation rate should be modified. The influence of premeiotic clusters is more obvious when the population size is small or the average cluster size is big. For example, if the population size is 3,000 and average cluster size is two, instead of one, the mutation rate is increased by about 9.4%.

Alleles↗
PubMed2002

Studies of FLT3 mutations in paired presentation and relapse samples from patients with acute myeloid leukemia: implications for the role of FLT3 mutations in leukemogenesis, minimal residual disease detection, and possible therapy with FLT3 inhibitors.

FLT3 mutations, either internal tandem duplications (ITDs) or aspartate residue 835 (D835) point mutations, are present in approximately one third of patients with acute myeloid leukemia (AML) and have been associated with an increased relapse rate. We have studied FLT3 mutations in paired presentation and relapse samples to ascertain the biology of these mutations and to evaluate whether they can be used as markers of minimal residual disease. At diagnosis, 24 patients were wild-type FLT3, and 4 acquired a FLT3 mutation at relapse (2 D835(+), 2 ITD(+)), with a further patient acquiring an ITD at second relapse. Of 20 patients positive at diagnosis (18 ITD(+), 2 D835(+)), 5 who were all originally ITD(+) had no detectable mutation at relapse, as determined by a sensitive radioactive polymerase chain reaction. One of these patients had acquired an N-Ras mutation not detectable at presentation. Furthermore, another patient had a completely different ITD at relapse, which could not be detected in the presentation sample. These results indicate that FLT3 mutations are secondary events in leukemogenesis, are unstable, and thus should be used cautiously for the detection of minimal residual disease.

Base Sequence↗
PubMed2003

Identification of a novel missense mutation that is as damaging to DAX-1 repressor function as a nonsense mutation.

Mutations in the DAX-1 (NROB1) gene result in X-linked congenital adrenal hypoplasia (AHC) and hypogonadotropic hypogonadism. The clinical presentation is usually as adrenal insufficiency in early life, with hypogonadotropic hypogonadism detected at the time of expected puberty. In this study we identified mutations in the DAX-1 gene of two patients with AHC. One mutation, Y399X, resulted in a premature stop codon and was associated with loss of Leydig cell responsiveness to human chorionic gonadotropin. The second, L297P, was a missense mutation, and human chorionic gonadotropin responsiveness was maintained. Kindred analysis established that the mutations had been inherited from the proband's mothers. The L297P has not been described previously and occurs within a highly conserved binding motif (LLXLXL). Transient transfection assays demonstrated that both mutations resulted in a severe loss of DAX-1 repressor activity. Immunohistochemical analysis of testicular tissue obtained from an affected sibling of the subject with the Y399X mutation, who had died with adrenal failure as a neonate, showed normal testicular morphology and expression of DAX-1, steroidogenic factor-1, and anti-Mullerian hormone protein. These data extend the clinical and molecular information on DAX-1 mutations, confirm normal testicular development at the neonatal stage, and illustrate variability in Leydig cell function.

Adrenal Glands↗
PubMed1990

Two unrelated patients with familial hyperproinsulinemia due to a mutation substituting histidine for arginine at position 65 in the proinsulin molecule: identification of the mutation by direct sequencing of genomic deoxyribonucleic acid amplified by polymerase chain reaction.

Mutations in the insulin gene can impair the bioactivity of the insulin molecule. Previously, two classes of mutations have been identified: 1) those that impair posttranslational processing of proinsulin to insulin, and 2) those that alter the structure of the insulin molecule, thereby reducing the affinity of the molecule for the insulin receptor. We have investigated two apparently unrelated patients, both of which have mutations that inhibit the conversion of proinsulin to insulin. By directly sequencing genomic DNA amplified by polymerase chain reaction, we have demonstrated that both patients are heterozygous for the same point mutation converting codon 65 from an arginine (CGT) to a histidine (CAT) codon. Because Arg65 is one of the two dibasic amino acids at the site of proteolytic cleavage between the insulin A-chain and C-peptide, this mutation explains the impairment in the cleavage of proinsulin to insulin. Interestingly, the same His65 mutation has been identified in the insulin gene of a Japanese kindred with familial hyperproinsulinemia. Thus, this mutation has occurred in three apparently unrelated kindreds from two different racial groups. This observation is consistent with the hypothesis that the dinucleotide sequence CpG, the first two nucleotides in the arginine (CGT) codon, is a "hot spot" for mutations.

Alleles↗
PubMed2001

Reversion of temperature-sensitive mutation by inhibition of proteasome-mediated degradation of mutated D123 protein.

A temperature-sensitive cell-cycle mutant of the 3Y1 rat fibroblast cell line, 3Y1tsD123 has in the D123 gene coding region a point mutation which causes instability of the D123 protein. Temperature-sensitive G1 arrest of the mutant is caused by increased degradation of the D123 protein at restrictive temperature. In this study we found that the selective proteasome inhibitors lactacystin and MG132 inhibited degradation of the mutated D123 protein in cell lines overexpressing the mutated D123 protein, followed by accumulation of a modified form (increased molecular weight other than by ubiquitination) of the D123 protein. Although a temperature-resistant revertant of the mutant had no further mutation in the D123 gene coding region, the modification of the mutated D123 protein was inhibited and the mutated D123 protein was rendered stable. The modification was also inhibited in the hybrid cell lines between the revertant and the cell line overexpressing the mutated D123 protein. These facts imply that the mutated D123 protein receives unidentified modification before degradation in the proteasome, and that the revertant expresses a gene inhibiting this modification.

Acetylcysteine↗
PubMed2007

Mutation scanning the GJB1 gene with high-resolution melting analysis: implications for mutation scanning of genes for Charcot-Marie-Tooth disease.

BACKGROUND: X-linked Charcot-Marie-Tooth type 1 disease has been associated with 280 mutations in the GJB1 [gap junction protein, beta 1, 32 kDa (connexin 32, Charcot-Marie-Tooth neuropathy, X-linked)] gene. High-resolution melting analysis with an automated instrument can be used to scan DNA for alterations, but its use in X-linked disorders has not been described. METHODS: A 96-well LightScanner for high resolution melting analysis was used to scan amplicons of the GJB1 gene. All mutations reported in this study had been confirmed previously by sequence analysis. DNA samples were amplified with the double-stranded DNA-binding dye LC Green Plus. Melting curves were analyzed as fluorescence difference plots. The shift and curve shapes of melting profiles were used to distinguish controls from patient samples. RESULTS: The method detected each of the 23 mutations used in this study. Eighteen known mutations provided validation of the high-resolution melting method and a further 5 mutations were identified in a blind study. Altered fluorescence difference curves for all the mutations were easily distinguished from the wild-type melting profile. CONCLUSION: High-resolution melting analysis is a simple, sensitive, and cost-efficient alternative method to scan for gene mutations in the GJB1 gene. The technology has the potential to reduce sequencing burden and would be suitable for mutation screening of exons of large multiexon genes that have been discovered to be associated with Charcot Marie Tooth neuropathy.

Charcot-Marie-Tooth Disease↗
PubMed2006

The influence of hitchhiking and deleterious mutation upon asexual mutation rates.

The question of how natural selection affects asexual mutation rates has been considered since the 1930s, yet our understanding continues to deepen. The distribution of mutation rates observed in natural bacteria remains unexplained. It is well known that environmental constancy can favor minimal mutation rates. In contrast, environmental fluctuation (e.g., at period T) can create indirect selective pressure for stronger mutators: genes modifying mutation rate may "hitchhike" to greater frequency along with environmentally favored mutations they produce. This article extends a well-known model of Leigh to consider fitness genes with multiple mutable sites (call the number of such sites alpha). The phenotypic effect of such a gene is enabled if all sites are in a certain state and disabled otherwise. The effects of multiple deleterious loci are also included (call the number of such loci gamma). The analysis calculates the indirect selective effects experienced by a gene inducing various mutation rates for given values of alpha, gamma, and T. Finite-population simulations validate these results and let us examine the interaction of drift with hitchhiking selection. We close by commenting on the importance of other factors, such as spatiotemporal variation, and on the origin of variation in mutation rates.

Models, Genetic↗
PubMed2000

A novel mutation of the ceruloplasmin gene in a patient with heteroallelic ceruloplasmin gene mutation (HypoCPGM).

We found a novel missense mutation in the ceruloplasmin (Cp) gene in a patient with the heteroallelic Cp gene mutation (HypoCPGM). The patient was a 72-year-old woman who came to our hospital with a 1-year history of postural tremor of the hands. The diagnosis was made based on serum Cp and copper readings which were about half the normal levels, as well as MRI tests of her brain which showed characteristics for hereditary ceruloplasmin deficiency (HCD), known to be caused by the homoallelic Cp gene mutation. Polymerase chain reaction (PCR)-direct sequencing analysis of the Cp gene of the patient revealed a novel point mutation, A to T, at nucleotide position 82 in Exon 1. This mutation changes the Ile28 codon (ATT) to a Phe codon (TTT) (missense mutation). PCR-restriction analysis with restriction enzyme Tsp EI for the mutation revealed that both the patient and her son were heterozygotes for the mutation.

Aged↗
PubMed2006

Assessing radiation-associated mutational risk to the germline: repetitive DNA sequences as mutational targets and biomarkers.

This review assesses recent data on mutational risk to the germline after radiation exposure obtained by molecular analysis of tandemly repeated DNA loci (TRDLs): minisatellites in humans and expanded simple tandem repeats in mice. Some studies, particularly those including exposure to internal emitters, indicate that TRDL mutation can be used as a marker of human radiation exposure; most human studies, however, are negative. Although mouse studies have suggested that TRDL mutation analysis may be more widely applicable in biomonitoring, there are important differences between the structure of mouse and human TRDLs. Mutational mechanisms probably differ between the two species, and so care should be taken in predicting effects in humans from mouse data. In mice and humans, TRDL mutations are largely untargeted with only limited evidence of dose dependence. Transgenerational mutation has been observed in mice but not in humans, but the mechanisms driving such mutation transmission are unknown. Some minisatellite variants are associated with human diseases and may affect gene transcription, but causal relationships have not yet been established. It is concluded that at present the TRDL mutation data do not warrant a dramatic revision of germline or cancer risk estimates for radiation.

Animals↗
PubMed2004

A novel highly pathogenic Alzheimer presenilin-1 mutation in codon 117 (Pro117Ser): Comparison of clinical, neuropathological and cell culture phenotypes of Pro117Leu and Pro117Ser mutations.

A novel presenilin-1 (PS1) mutation (P117S) in an American pedigree is described. We compare clinical, neuropathological and cell culture phenotypes produced by this mutation with another codon 117 mutation that was earlier discovered by our group in a Polish kindred. Both mutations are associated with an unusually severe Alzheimer disease (AD) phenotype, with the onset starting before the third decade of life, rapid disease progression and acute presentation of clinical symptoms. The severity of clinical phenotype was closely correlated with the abundance of pathology: massive deposition of Abeta42 in plaques, severe neurofibrillary degeneration and neuronal loss. When overexpressed in mouse neuroblastoma N2a cells, both mutations caused loss of an ability to promote neurite outgrowth and produced an increase in the ratio of secreted Abeta42/40 amyloid peptides. In stably transfected N2a cell lines only mutant proteins were endoproteolytically cleaved indicating some dependability of this process on the presence of mutation. Taken together, our results show that clinical and cell culture phenotypes produced by these 2 codon 117 mutations are closely related suggesting that the pathogenic action of PS1 may involve effect on neurite outgrowth and endoproteolytic cleavage of the full-length protein. Given the high potency in vivo and in vitro of both codon 117 mutations, this site of PS1 must be particularly important for its normal/pathogenic function.

Adult↗