Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Point 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.

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

At least 19 recordsLinked to original sources
PubMed1994

Predicting local structural changes that result from point mutations.

Point mutations are frequently used to explore the structure and/or function of proteins. The ability to predict the structural effects of point mutations would make the planning of such experiments more reliable. We have now derived a set of detailed predictive rules based on the comparison of crystal structures of point mutants and wild types in 83 cases. Despite the surprising simplicity of these rules, they describe well the conformational changes in 85% of all point mutant structures available at present.

Amino Acid Sequence↗
PubMed1982

Extrachromosomal mutator inducing point mutations and deletions in mitochondrial genome of fission yeast.

We report the isolation and characterization of a mutator mutant in the fission yeast Schizosaccharomyces pombe. This mutator is of extrachromosomal, very likely mitochondrial, inheritance and acts exclusively on mitochondrial mtDNA. It greatly enhances the frequency of spontaneous mitochondrial drug-resistance mutants compared to the wild type, but it is not obligatory for their occurrence. In contrast, mitochondrial respiratory deficient mutants can only be isolated from mutator strains. It could be shown that this mutator induces point mutations as well as deletions in the mitochondrial genome which lead to respiratory deficiency. This mutator might prove to have a novel function encoded by the mtDNA.

Anti-Bacterial Agents↗
PubMed1994

Radiation-induced point mutations, deletions and micronuclei in lacI transgenic mice.

Ionizing radiation induces gene mutations (point mutations, deletions and insertions) as well as chromosome damage in mammalian cells. Although these effects have been studied extensively in cells in culture, until recently it has not been possible to analyze the mutagenic potential of ionizing radiation in vivo, especially at the molecular level. The development of transgenic mutagenesis systems has now made it possible to study the effects of ionizing radiation at both the molecular and chromosomal levels in the same animal. In this report we present preliminary data on the response of Big Blue lacI transgenic mice to ionizing radiation as measured by lacI mutations and micronuclei. C57Bl/6 transgenic mice were irradiated with 137Cs gamma-rays at doses ranging from 0.1 to 14 Gy, and expression times ranging from 2 to 14 days. Dose-related increases in the mutant frequency were observed after irradiations with longer expression times. Mutant plaques were analyzed by restriction enzyme digestion to detect large structural changes in the target sequence. Of 34 gamma-ray-induced mutations analyzed, 4 were large-scale rearrangements. 3 of these rearrangements were deletions within the lacI gene characterized by the presence of short regions of homology at the breakpoint junctions. The fourth rearrangement was a deletion that extended from within the alpha lacZ gene into downstream sequences and that had 43 bp of homology at the junction. These data indicate that the Big Blue lacI transgenic mouse system in sensitive to the types of mutations induced by ionizing radiation. To determine whether the presence of the transgene affects micronucleus induction we compared the response of nontransgenic to hemizygous transgenic B6C3F1 mice and the response of nontransgenic to hemizygous and homozygous transgenic C57Bl/6 mice. The presence or absence of the lacI transgene had no effect on spontaneous micronucleus frequencies for either strain. However, radiation-induced micronucleus frequencies were significantly higher in hemizygous lacI B6C3F1 mice than in nontransgenic litter mates; the converse was true in C57Bl/6 mice. These data suggest that the lacI transgene does not cause chromosome instability as measured by spontaneous micronucleus levels. However, the response of these transgenic mice to a variety of clastogenic agents needs to be investigated before they are integrated into standard in vivo assays for chromosome damage.

Animals↗
PubMed1994

On the origin of deletions and point mutations in Duchenne muscular dystrophy: most deletions arise in oogenesis and most point mutations result from events in spermatogenesis.

We present the results of a study of the rate and origin of mutations in Duchenne muscular dystrophy (DMD). Depending on the type of mutation (deletion/duplication or point mutation) present in the patient, there are widely varying ratios of male to female mutation rates. In deletions, the male mutation rate is only 30% of the female one. In non-deletional/non-duplicational mutations (presumably containing a high proportion of point mutations) the male mutation rate is at least 2.2 as high as the female one and probably much higher. Allowing for the presence of autosomal recessive phenocopies we find that k in non-deletional/non-duplicational mutations is 40.3. These findings mean that the vast majority of deletions arise in oogenesis, while most point mutations stem from spermatogenesis. Previous investigations have shown that in other diseases and genes, most notably haemophilia B and A, but also the ZFY and ZFX genes, the male mutation rate for point mutations tends to be higher than the female one. Our results can be seen as a confirmation of this for the special case of DMD. The influence on risk figures is considerable. As an example, the risk of the mother of an isolated case of DMD without an apparent structural anomaly of the gene of being a carrier increases from 67% to at least 76%. Given the estimate of 40.3 for k, allowing for the presence of autosomal recessive phenocopies mentioned above, it increases even further to 98%. However, as confidence intervals are still large, more data are needed to improve the estimates. Germinal mosaicism in this context is discussed.

Fathers↗
PubMed1995

Detection of point mutations in chloroplast genes of Antirrhinum majus L. I. Identification of a point mutation in the psaB gene of a photosystem I plastome mutant.

A point mutation in the plastome-encoded psaB gene of the mutant en:alba-1 of Antirrhinum majus L. was identified by an analysis of chloroplast DNA with a modified PCR-SSCP technique. Application of this technique is indicated when a gene or a group of genes is known in which the point mutation is located. Analysis of primary photosynthetic reactions in the yellowish white plastome mutant indicated a dysfunction of photosystem (PS) I. The peak wavelength of PS I-dependent chlorophyll (Chl) fluorescence emission at 77 K was shifted by 4 nm to 730 nm, as compared to fluorescence from wild-type. There were no redox transients of the reaction center Chl P700 upon illumination of leaves with continuous far-red light or with rate-saturating flashes of white light. The PS I reaction center proteins PsaA and PsaB are not detectable by SDS-PAGE in mutant plastids. Hence, plastome encoded PS I genes were regarded as putative sites of mutation. In order to identify plastome mutations we developed a modified SSCP (single-strand conformation polymorphism) procedure using a large PCR fragment which can be cleaved with various restriction enzymes. When DNA from wild-type and en:alba-1 was submitted to SSCP analysis, a single stranded HinfI fragment of a PCR product of the psaB gene showed differences in electrophoretic mobility. Sequence analysis revealed that the observed SSCP was caused by a single base substitution at codon 136 (TAT-->TAG) of the psaB gene. The point mutation produces a new stop codon that leads to a truncated PsaB protein. The results presented indicate that the mutation prevents the assembly of a functional PS I complex. The applicability to other plastome mutants of the new method for detection of point mutations is discussed.

Amino Acid Sequence↗
PubMed1993

Amplification of c-MYC oncogene and point mutation of N-RAS oncogene point mutation in acute myelocytic leukemias with double minute chromosomes.

Two patients with acute myelocytic leukemia (AML) showing double minute (dmin) chromosomes were analysed to identify oncogene activation. Cytogenetic analysis showed 1-53 dmin chromosomes with the normal karyotype in the first patient and 1-84 dmin chromosomes with complex chromosome aberrations. Analysis of DNA from two patients revealed five- to tenfold amplification of c-MYC oncogene in the leukemic cells. The other sixteen oncogenes studied showed no increase in the gene content. Furthermore, a transforming gene, N-RAS was detected in the first patient by nude mouse tumorigenicity assay (in vivo selection assay). These results suggest that the amplification of c-MYC gene is common in dmin-positive AML patients and co-ordination of c-MYC and N-RAS oncogene might also play a significant role in the pathogenesis of some AML patients.

Aged↗
PubMed1995

DNA binding capacity of the WT1 protein is abolished by Denys-Drash syndrome WT1 point mutations.

Constitutional point mutations in the zinc finger (ZF) region of the Wilms' tumour suppressor gene 1 (WT1) lead to Denys-Drash syndrome (DDS). Patients with this syndrome display renal failure, Wilms' tumour (WT) and pseudohermaphroditism. DDS WT1 mutations fall into three major categories: (a) missense mutations altering amino acids which directly interact with the DNA target; (b) substitution of amino acids involved in zinc complexing; and (c) nonsense mutations leading to the removal of at least two zinc fingers. We have expressed the WT1 zinc fingers as glutathione-S-transferase fusion proteins, with the lysine-threonine-serine (KTS) alternate splice between ZF3 and ZF4 either present or absent. WT1 fusion constructs with all three classes of DDS mutation were also created. Wild-type and mutant fusion proteins were assayed for their DNA-binding affinity using four previously identified WT1 DNA targets: an EGR1 consensus site; murine insulin-like growth factor 2 promoter 2 (IGF2P2); a (TCC)n motif from the PDGFA-chain promoter; and +P5, a genomic fragment isolated by its affinity for WT1 + KTS. WT1-KTS bound all four targets, but WT1 + KTS only bound +P5. All three classes of DDS mutation investigated, with or without KTS, abolished binding to all four targets. This provides evidence that DDS mutations act either as dominant-negative antimorphs, or elicit their effect through disturbed isoform dosage balance.

Abnormalities, Multiple↗
PubMed1993

A point mutation found in the WT1 gene in a sporadic Wilms' tumor without genitourinary abnormalities is identical with the most frequent point mutation in Denys-Drash syndrome.

We have analyzed exon 9 of the WT1 gene of 18 non-familial/sporadic unilateral Wilms' tumors (WTs) from Japanese patients, by the polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) method. After screening these WTs, a nucleotide alternation, which was present on both alleles, was found in only one case. Furthermore, PCR-SSCP analysis of the constitutional DNA revealed that this patient carried the mutation on only one allele in the germline. Sequence analysis showed that the tumor carried a point mutation (C-1180 to T-1180) in WT1 exon 9 of both alleles, resulting in an Arg-394 to Trp-394 amino acid substitution within the third zinc finger domain of the WT1 product. Interestingly, this mutation is identical with the most frequent point mutation associated with the Denys-Drash syndrome. However, the classical triad of Denys-Drash syndrome does not apply to this patient. This is in the first report of the point mutation in the zinc finger domain of both WT1 alleles in a sporadic unilateral WT without genitourinary abnormalities, and the mutation suggests that some sporadic WTs carry the Denys-Drash WT1 mutations.

Base Sequence↗
PubMed1996

Detection of K-ras point mutations at codon 12 in pancreatic juice for the diagnosis of pancreatic cancer by hybridization protection assay: a simple method for the determination of the types of point mutation.

The present study was undertaken to detect K-ras oncogene point mutations at codon 12 in pure pancreatic juice (PPJ) by the hybridization protection assay (HPA) method for the diagnosis of pancreatic cancer (PC). This assay can be carried out within 30 min and can determine not only the presence of a mutation, but also the mutational type of K-ras at codon 12. The minimal ratio of mutant DNA detectable by the HPA was 5-10% of the total DNA. PPJ was collected through a cannula under duodenal fiberscope control from 20 patients with PC and 20 patients with chronic pancreatitis (CP). Analysis of PPJ by the HPA revealed that the incidence of K-ras point mutations at codon 12 was 55% (11/20) in patients with PC and 0% (0/20) in those with CP. Mutational types of K-ras at codon 12 in PC were aspartic acid (Asp) in nine cases, both Asp and cysteine in one case, and arginine in one case. Analysis of K-ras point mutations at codon 12 in PPJ using the HPA method seems promising as a new genetic test for the diagnosis of PC, because the HPA method is simple, and can easily determine the mutational type.

Base Sequence↗
PubMed1991

Mutations of the P53 gene, including an intronic point mutation, in colorectal tumors.

In this study, analysis of structural changes of the p53 gene in colorectal tumors revealed point mutations detected in 8 of 14 carcinomas and 2 of 2 adenomas. Of these 10 cases with point mutations, eight had one or more missense mutations, one had a nonsense mutation, and the remaining one had, interestingly, an intronic point mutation with subsequent activation of a cryptic splice donor site in the flanking exon. This report contains the first identification of an intronic point mutation of the p53 gene in a colorectal cancer case.

Amino Acid Sequence↗
PubMed1994

Structure and function in rhodopsin. 7. Point mutations associated with autosomal dominant retinitis pigmentosa.

Autosomal dominant retinitis pigmentosa (ADRP) is a hereditary form of retinitis pigmentosa which accounts for about 15% of all types of the latter disease. Recently, close to 50 mutations, mostly point mutations, have been identified in the rhodopsin gene in ADRP patients. We have introduced these mutations in the synthetic bovine rhodopsin gene and herein report on the expression of the mutant genes in COS-1 cells and studies in vitro of the properties of the expressed opsins. The mutant phenotypes fall into three classes: Class I mutants are expressed in COS-1 cells at wild-type levels, form the normal rhodopsin chromophore with 11-cis-retinal, and are transported to the cell surface. However, on illumination, they activate transducin inefficiently. Class II mutants remain in the endoplasmic reticulum and do not bind 11-cis-retinal to form the chromophore. Class III mutants are expressed at low levels and form rhodopsin chromophore only poorly. They also remain in the endoplasmic reticulum and, as expected, show high mannose glycosylation. Nearly all of the mutants studied show abnormal sensitivity to light compared to the wild type, and they activate transducin less efficiently. We conclude that the majority of the ADRP mutants have folding defects.

Amino Acid Sequence↗
PubMed1995

Leber's hereditary optic neuropathy plus dystonia is caused by a mitochondrial DNA point mutation.

A novel point mutation in the ND6 subunit of complex I at position 14,459 of the mitochondrial DNA (MTND6*LDY T14459A) was identified as a candidate mutation for the highly tissue-specific disease. Leber's hereditary optic neuropathy plus dystonia. Since the MTND6*LDYT14459A mutation was identified in a single family, other pedigrees with the mutation are needed to confirm its association with the disease. Clinical, biochemical, and genetic characterization is reported in two additional pedigrees. Leber's hereditary optic neuropathy developed in two family members in one pedigree. The daughter had clinically silent basal ganglia lesions. In a second pedigree, a single individual presented with childhood-onset generalized dystonia and bilateral basal ganglia lesions. Patient groups that included individuals with Leigh's disease, dystonia plus complex neurodegeneration, and Leber's hereditary optic neuropathy did not harbor the MTND6*LDYT14459A mutation, suggesting that this mutation displays a high degree of tissue specificity, thus producing a narrow phenotypic range. These results confirm the association of the MTND6*LDYT14459A mutation with Leber's hereditary optic neuropathy and/or dystonia. As the first genetic abnormality that has been identified to cause generalized dystonia, this mutation suggests that nuclear DNA or mitochondrial DNA mutations in oxidative phosphorylation genes are important considerations in the pathogenesis of dystonia.

Adolescent↗
PubMed1982

Phenotypic reversion of an IS1-mediated deletion mutation: a combined role for point mutations and deletions in transposon evolution.

We have physically characterised a deletion mutant of the R plasmid R100 which has lost all of the antibiotic resistances, including chloramphenicol resistance (Cmr), coded by its IS1-flanked r-determinant. The deletion was mediated by one of the flanking IS1 elements and terminates within the carboxyl terminus of the Cmr gene. DNA sequence analysis showed that the mutated gene would produce a protein 20 amino acids longer than the wild-type due to fusion with an open reading frame in the IS element. Surprisingly for a deletion mutation, rare, spontaneous Cmr revertants could be recovered. Two of the four revertants studied had frame shifts due to the insertion of a single AT base pair at the same position; the revertants would code for a protein five amino acids shorter than the wild-type. The other two revertants had acquired duplications of the 34-bp inverted terminal repeat sequences of the IS1 element and would direct the synthesis of a protein six amino acids longer than the wild-type. The reverted Cmr markers were still capable of transposition. These observations suggest a role for point mutations and small DNA rearrangements in the formation of new gene organisations produced by mobile genetic elements.

Base Sequence↗
PubMed1992

Cholangiocarcinomas in Japanese and Thai patients: difference in etiology and incidence of point mutation of the c-Ki-ras proto-oncogene.

Point-mutational activation of the c-Ki-ras proto-oncogene has been shown to be rare in human hepatocellular carcinoma, the most common primary liver cancer and one usually associated with chronic viral infection. To reveal the association of c-Ki-ras activation with cholangiocarcinogenesis under different etiological backgrounds, the incidence of point mutation at codons 12 and 13 of the c-Ki-ras proto-oncogene was examined in three groups of human liver cancers with differentiation to biliary epithelial cells: Group 1, cholangiocellular carcinoma in Japanese with normal livers; Group 2, cholangiocellular carcinoma in Thais who had lived in an area where the liver fluke Opisthorchis viverrini is endemic; and Group 3, combined hepatocellular-cholangiocellular carcinoma, a rare type showing features of both hepatocellular and biliary epithelial differentiation, in Japanese with chronic viral hepatitis with or without cirrhosis. The polymerase chain reaction and direct sequencing of its product were used to detect the mutation. Point mutation at codon 12 of the c-Ki-ras gene was detected in five (56%) of nine cases in Group 1. In contrast, the mutation was not detected in any of the cases in Groups 2 and 3. Therefore, point-mutational activation of c-Ki-ras did not seem to be involved in the development of primary liver cancers associated with apparent chronic irritation of liver cells or biliary epithelial cells caused by exogenous liver-fluke or viral infection. On the other hand, point-mutational activation of the c-Ki-ras proto-oncogene may be involved in cholangiocarcinogenesis in liver without preexisting liver-fluke or viral infection.

Adenoma, Bile Duct↗
PubMed1993

Sequencing analysis of mutation points in the biotin operon of biotin-overproducing Escherichia coli mutants.

We analyzed mutation points of the biotin operon from biotin-overproducing mutants of Escherichia coli resistant to two biotin analogs, actithiazic acid and 5-(2-thienyl)-valeric acid, by DNA sequencing. The biotin operons cloned from these mutants were classified into three groups. One point mutation, which was a GC-->AT change within the operator overlapping the -10 region of the rightward (bioB) promoter, was considered to result in disruption of operator structure and enhancement of promoter activity. Two other point mutations, which were both GC-->AT changes just before and after the initiation codon of the bioB gene, were considered to activate the translation efficiency. These mutations significantly accelerated the biotin-forming activity from dethiobiotin in cell-free extracts.

Base Sequence↗
PubMed1996

Clinical heterogeneity associated with the mitochondrial DNA T8993C point mutation.

The mitochondrial DNA (mtDNA) point mutation T8993G has been associated with maternally inherited Leigh syndrome (MILS) when very abundant (> 95%). MILS patients are usually severely affected and die in early infancy. In 1993, a novel T8993C point mutation was described in a juvenile form of Leigh syndrome (LS) characterized by a less aggressive clinical course. We describe four unrelated T8993C patients who had diverse, relatively mild, clinical manifestations. Polymerase chain reaction-restriction fragment length polymphorphism analysis showed that the heteroplasmic T8993C point mutation was very abundant in several tissues from all four patients (94.2 +/- 1.5%) but was less copious in blood from 20 maternal relatives. ATP production in mitochondria isolated from skin fibroblasts in three patients was normal, whereas in one patient it was decreased to 20-35% of controls. These findings suggest that the T8993C mutation is less severe than the more common T8993G mutation.

Adenosine Triphosphate↗
PubMed1992

Mutational spectrometry: a general approach for hot-spot point mutations in selectable genes.

To observe point mutational spectra with a high degree of precision, independent large cultures of human lymphoblastoid cells were treated with a mutagen, benzo[a]pyrene diol epoxide, and mutants at the HPRT gene were selected en masse by 6-thioguanine resistance. An average of 1.6 x 10(4) 6-thioguanine-resistant mutants were created per experiment and the kinds, positions, and numbers of the most frequent mutations were examined in exon 3 of the HPRT gene by using a high-fidelity polymerase chain reaction and denaturing gradient gel electrophoresis. Sixteen exon 3-specific mutations were found to be predominantly G----T transversions and corresponded to an average of 3500 induced mutants per experiment. Of these mutations, 6 occurred within a run of 6 guanines and 5 occurred in the sequence 5'-GAAGAG-3'. The variation among independent experiments is consistent with the numerical expectation that all 16 mutations fulfill reasonable statistical criteria for mutational hot spots. The agreement with data from various systems using clone-by-clone analysis shows that the protocol reported herein can be a useful tool to study hot-spot point mutational spectra for DNA sequences for which phenotypic selection systems exist.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗