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 1,351 records · Page 75Linked to original sources
PubMed2006

A single P-loop glutamate point mutation to either lysine or arginine switches the cation-anion selectivity of the CNGA2 channel.

Cyclic nucleotide-gated (CNG) channels play a critical role in olfactory and visual transduction. Site-directed mutagenesis and inside-out patch-clamp recordings were used to investigate ion permeation and selectivity in two mutant homomeric rat olfactory CNGA2 channels expressed in HEK293 cells. A single point mutation of the negatively charged pore loop (P-loop) glutamate (E342) to either a positively charged lysine or arginine resulted in functional channels, which consistently responded to cGMP, although the currents were generally extremely small. The concentration-response curve of the lysine mutant channel was very similar to that of wild-type (WT) channels, suggesting no major structural alteration to the mutant channels. Reversal potential measurements, during cytoplasmic NaCl dilutions, showed that the lysine and the arginine mutations switched the selectivity of the channel from cations (P(Cl)/P(Na) = 0.07 [WT]) to anions (P(Cl)/P(Na) = 14 [Lys] or 10 [Arg]). Relative anion permeability sequences for the two mutant channels, measured with bi-ionic substitutions, were NO(3)(-) > I(-) > Br(-) > Cl(-) > F(-) > acetate(-), the same as those obtained for anion-selective GABA and glycine channels. The mutant channels also seem to have an extremely small single-channel conductance, measured using noise analysis of about 1-2 pS, compared to a WT value of about 29 pS. The results showed that it is predominantly the charge of the E342 residue in the P-loop, rather than the pore helix dipoles, which controls the cation-anion selectivity of this channel. However, the outward rectification displayed by both mutant channels in symmetrical NaCl solutions suggests that the negative ends of the pore helix dipoles may play a role in reducing the outward movement of Cl(-) ions through these anion-selective channels. These results have potential implications for the determinants of anion-cation selectivity in the large family of P-loop-containing channels.

Amino Acid Sequence↗
PubMed1997

Haemophilia B in female twins caused by a point mutation in one factor IX gene and nonrandom inactivation patterns of the X-chromosomes.

Haemophilia B is a X-linked recessive bleeding disorder with an incidence of 1:25,000-30,000 male birth. Usually female carriers are clinically normal. Phenotypic expression of the disease in female carriers is extremely rare. We describe cytogenetically inconspicuous female identical twins both with factor IX levels below 2%, prolonged bleeding after venipuncture as well as haematomas after intramuscular injections. The father, suffering from a severe haemophilia B, is deceased. By sequencing one point mutation was characterized in heterozygote condition in the factor IX gene of the probands at nt 17678. This mutation leads to the substitution cystein 88 to tyrosine in the growth factor domain of the factor IX. Investigation of the X-chromosomal inactivation by comparison of methylation patterns of genomic DNA at locus DXS255 after digestion with Pst I and Pst I +Hha I and hybridisation with the probe M27beta indicated a nonrandom pattern of X-chromosomal inactivation in the twins. In both girls, only the paternal X-chromosome was the active one leading to the phenotypic expression of haemophilia in the female carriers.

Blood Coagulation Tests↗
PubMed1998

Point mutations in the integron integrase IntI1 that affect recombination and/or substrate recognition.

The site-specific recombinase IntI1 found in class 1 integrons catalyzes the excision and integration of mobile gene cassettes, especially antibiotic resistance gene cassettes, with a site-specific recombination system. The integron integrase belongs to the tyrosine recombinase (phage integrase) family. The members of this family, exemplified by the lambda integrase, do not share extensive amino acid identities, but three invariant residues are found within two regions, designated box I and box II. Two conserved residues are arginines, one located in box I and one in box II, while the other conserved residue is a tyrosine located at the C terminus of box II. We have analyzed the properties of IntI1 variants carrying point mutations at the three conserved residues of the family in in vivo recombination and in vitro substrate binding. We have made four proteins with mutations of the conserved box I arginine (R146) and three mutants with changes of the box II arginine (R280); of these, MBP-IntI1(R146K) and MBP-IntI1(R280K) bind to the attI1 site in vitro, but only MBP-IntI1(R280K) is able to excise cassettes in vivo. However, the efficiency of recombination and DNA binding for MBP-IntI1(R280K) is lower than that obtained with the wild-type MBP-IntI1. We have also made two proteins with mutations of the tyrosine residue (Y312), and both mutant proteins are similar to the wild-type fusion protein in their DNA-binding capacity but are unable to catalyze in vivo recombination.

Amino Acid Sequence↗
PubMed1999

Characterization of point mutations in patients with pyruvate dehydrogenase deficiency: role of methionine-181, proline-188, and arginine-349 in the alpha subunit.

Human pyruvate dehydrogenase (E1), a heterotetramer (alpha2beta2), is the first component of the pyruvate dehydrogenase complex (PDC). E1 catalyzes the thiamin pyrophosphate (TPP)-dependent decarboxylation of pyruvate and the reductive acetylation of the dihydrolipoamide acetyltransferase component. Site-directed mutagenesis was employed to recreate three point mutations in the alpha subunit identified in E1-deficient patients, M181V, R349H, and P188L (P188A mutant E1 was used because of the very low level of expression of P188L), to investigate the functional roles of these three amino acid residues. P188A mutant E1 was much less thermostable than the wild-type E1. The kcats of M181V and P188A mutant E1s determined in the PDC reaction were 38 and 24% of that of the wild-type enzyme, respectively. The apparent Km for TPP for M181V increased significantly (approx 250-fold when determined in the PDC assay), while the apparent Km for pyruvate increased by only about 3-fold. In contrast, P188A had similar Kms for the coenzyme and the substrate as the wild-type. Km values for R349H were not determined due to the extremely low activity of this mutant (1.2% of the wild-type E1-specific activity measured in the PDC assay). Wild-type E1 displayed a lag phase in the progress curve of the PDC reaction measured in the presence of low TPP concentrations (below 1 microM) only. All mutants had a lag phase that was not eliminated even at very high TPP concentrations, suggesting modifications in the conformation of the active site. Kinetic analysis indicated thiamin 2-thiothiazolone pyrophosphate (ThTTPP) to be an intermediate analog for wild-type human E1. M181V required a higher concentration of ThTTPP for inactivation than the wild-type and P188A E1s. The results of circular dichroism spectropolarimetry in the far UV region indicated that there were no major changes in the secondary structure of M181V, P188A, and R349H E1s. These mutant enzymes exhibited negative dichroic spectra at about 330 nm only in the presence of high TPP concentrations. This study suggests that arginine-349 is critical for E1's activity, methionine-181 is involved in the binding of TPP, and proline-188 is necessary for structural integrity of E1.

2,6-Dichloroindophenol↗
PubMed2000

A point mutation in PTPRC is associated with the development of multiple sclerosis.

Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system. It is widely accepted that a dysregulated immune response against brain resident antigens is central to its yet unknown pathogenesis. Although there is evidence that the development of MS has a genetic component, specific genetic factors are largely unknown. Here we investigated the role of a point mutation in the gene (PTPRC) encoding protein-tyrosine phosphatase, receptor-type C (also known as CD45) in the heterozygous state in the development of MS. The nucleotide transition in exon 4 of the gene locus interferes with mRNA splicing and results in altered expression of CD45 isoforms on immune cells. In three of four independent case-control studies, we demonstrated an association of the mutation with MS. We found the PTPRC mutation to be linked to and associated with the disease in three MS nuclear families. In one additional family, we found the same variant CD45 phenotype, with an as-yet-unknown origin, among the members affected with MS. Our findings suggest an association of the mutation in PTPRC with the development of MS in some families.

Base Sequence↗
PubMed1996

Activation of phosphoinositide 3-kinase by interaction with Ras and by point mutation.

We have reported previously that Ras interacts with the catalytic subunit of phosphoinositide 3-kinase (PI 3-kinase) in a GTP-dependent manner. The affinity of the interaction of Ras-GTP with p85alpha/p110alpha is shown here to be approximately 150 nM. The site of interaction on the p110alpha and beta isoforms of PI 3-kinase lies between amino acid residues 133 and 314. A point mutation in this region, K227E, blocks the GTP-dependent interaction of PI 3-kinase p110alpha with Ras in vitro and the ability of Ras to activate PI 3-kinase in intact cells. In addition, this mutation elevates the basal activity of PI 3-kinase in intact cells, suggesting a direct influence of the Ras binding site on the catalytic activity of PI 3-kinase. Using an in vitro reconstitution assay, it is shown that the interaction of Ras-GTP, but not Ras-GDP, with PI 3-kinase leads to an increase in its enzymatic activity. This stimulation is synergistic with the effect of tyrosine phosphopeptide binding to p85, particularly at suboptimal peptide concentrations. These data show that PI 3-kinase is regulated by a number of mechanisms, and that Ras contributes to the activation of this lipid kinase synergistically with tyrosine kinases.

1-Phosphatidylinositol 4-Kinase↗
PubMedDate not supplied

Associations of antifolate resistance in vitro and point mutations in dihydrofolate reductase and dihydropteroate synthetase genes of Plasmodium falciparum.

BACKGROUND: Antifolate antimalarials like sulfadoxine-pyrimethamine are used as second-line treatment for Plasmodium falciparum malaria patients who fail to respond to chloroquine. The efficacy of the sulfa-pyrimethamine combination in the treatment is also compromised by the development of resistance in the parasite. Resistance to these drugs has been shown to encode with point mutations in dihydrofolate reductase and dihydropteroate synthetase genes. SETTINGS: An experimental study. MATERIAL AND METHODS: Forty clinical isolates collected from different geographical locations in India were used to assess the relationships between resistance to sulfadoxine-pyrimethamine (SP) and mutations in P. falciparum dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS). In vitro drug susceptibility and mutation-specific polymerase chain reaction (PCR) assays were also done. RESULTS: It was observed that a number of isolates possessed mutant genotypes and showed low sensitivity to SP in vitro. Of the 40 clinical isolates studied, 87.5% had DHFR and 15% had DHPS gene mutations. As observed from PCR results, 55( (22/40) presented double mutation of DHFR Arg-59 and Asn-108 and 32.5 % (13/40) had single mutant type allele of Asn-108. Of the 40 isolates, 10 % (4/40) presented doubly mutated forms of DHPS Phe-436 and Thr-613 and single mutant type allele Gly-581 was detected in 5 % (2/40) isolates. Parasites carrying double or single mutant forms of DHFR/DHPS showed elevated minimum inhibitory concentration (MIC) values of both pyrimethamine (760-6754 nM; r=0.69) and sulfadoxine (108 - 540 micro M; r=0.87) when compared to sensitive and resistant strains. CONCLUSION: Though there was a correlation between molecular techniques and in vitro drug sensitivity profiles, the relevance of these findings to the clinical efficacy of SP combination drugs needs to be established by controlled clinical trials.

Adolescent↗
PubMed1998

[Four novel point mutations of factor IX gene detected by denaturing gradient gel electrophoresis].

OBJECTIVE: To identify factor IX gene mutations in patients with hemophilia B. METHODS: The coding regions, splicing junction sites and part of the 5' and 3' flanking regions of factor IX gene were screened by polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). RESULTS: Four amplified fragments showed abnormal electrophoresis patterns, and sequencing of them demonstrated four novel point mutations including a T to G transition at nucleotide 10,380 resulting in intron 3 covering the splicing site, a A to G transition at nucleotide 30,918 resulting in a substitution of Cys for Tyr at codon 266 in exon 8, and a A to C transition at nucleotide 31,007 resulting in a substitution of Pro for Thr at codon 299 in exon 8. CONCLUSION: Detection of mutations by PCR, DGGE and sequencing was useful not only for understanding the structure function relationship of F IX, but also for the carrier detection and prenatal diagnosis.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2000

Correlation between point mutations in NS2 and the viability and cytopathogenicity of Bovine viral diarrhea virus strain Oregon analyzed with an infectious cDNA clone.

Cytopathogenicity of Bovine viral diarrhea virus (BVDV) is correlated with expression of the nonstructural protein NS3, which can be generated by processing of a fusion protein termed NS2-3. For the cytopathogenic (cp) BVDV strain Oregon, NS2-3 processing is based on a set of point mutations within NS2. To analyze the correlation between NS2-3 cleavage and cytopathogenicity, a full-length cDNA clone composed of cDNA from BVDV Oregon and the utmost 5'- and 3'-terminal sequences of a published infectious BVDV clone was established. After transfection of RNA transcribed from this cDNA clone, infectious virus with similar growth characteristics to wild-type BVDV Oregon could be recovered that also exhibited a cytopathic effect. Based on this cDNA construct and published cp and noncp infectious clones, chimeric full-length cDNA clones were constructed. Analysis of the recovered viruses demonstrated that the presence of the NS2 gene of BVDV Oregon in a chimeric construct is sufficient for NS2-3 processing and a cp phenotype. Since previous studies had revealed that the amino acid serine at position 1555 of BVDV Oregon plays an important role in efficient NS2-3 cleavage, mutants of BVDV Oregon with different amino acids at this position were constructed. Some of these mutants showed NS2-3 cleavage efficiencies in the range of the wild-type sequence and allowed the recovery of viruses that behaved similarly to wild-type virus with regard to growth characteristics and cytopathogenicity. In contrast, other mutants with considerably reduced NS2-3 cleavage efficiencies propagated much more slowly and reverted to viruses expressing polyproteins with sequences allowing efficient NS2-3 cleavage. These viruses apparently induced cytopathic effects only after reversion.

Animals↗
PubMed2002

Comparative potencies of induction of point mutations and genetic duplications by the methylating agents methylazoxymethanol and dimethyl sulfate in bacteria.

Methylazoxymethanol (MAM) and dimethyl sulfate (DMS) are mutagens whose genetic effects can be ascribed to the methylation of DNA. While both methylate the N7 position of guanine heavily, only MAM strongly methylates the O(6) position of guanine. We evaluated the relative effectiveness and specificity of MAM and DMS in bacterial assays for the induction of point mutations and the formation of chromosomal duplications by genetic recombination. Salmonella typhimurium strain TS1121 was used to measure the formation of genetic duplications on the basis of the aroC321 allele and mutations by reversion of the hisG46 allele. Specific base pair substitutions and frameshift mutations were measured in a reversion assay based on lacZ alleles of Escherichia coli. The results show MAM to be the more potent mutagen and DMS the stronger recombinagen in the Salmonella assay. In the lacZ assay DMS induced several classes of base pair substitutions (GC-->AT transitions, GC-->TA transversions and AT-->TA transversions), as well as lower frequencies of +1, -1 and -2 frameshift mutations. The activity of MAM as a base pair substitution mutagen was more specific than that of DMS, inducing only GC-->AT transitions. It also induced +G, -G, -A and -CG frameshift mutations, though more weakly than it induced GC-->AT transitions. Long known as a base pair substitution mutagen, the induction of frameshifts by MAM was unexpected. The results show that both DMS and MAM are effective inducers of base pair substitutions and modest inducers of frameshifts and that DMS exhibits a broader spectrum of mutagenic activity than does MAM.

Alleles↗
PubMed2000

Complex karyotype and N-RAS point mutation in a case of acute megakaryoblastic leukemia (M7) following a myelodysplastic syndrome.

The development of acute megakaryoblastic leukemia (ANLL-M7) following myelodysplastic syndrome (MDS) has been described only in a few reports, and the mutations necessary for this transformation are still unknown. In this study, we describe a case of ANLL-M7 with a previous history of MDS presenting a complex karyotype 46,XX, t(4;11)(q21;q23),del(5)(q13q33),t(12;13)(p13;q21) and N-RAS point mutation. During MDS, the patient showed a hypercellular myelogram with dysplasia of the three myeloid lineages and the clinical symptoms characteristic of the 5q- syndrome. During the follow-up, we observed the appearance of two additional subclones, one with an isochromosome 17q and another with polyploidy. The presence of an isochromosome 17q in one subclone and polyploidy in another is probably due to the genetic instability generated by the malignant transformation.

Chromosome Aberrations↗
PubMed1994

Leigh syndrome and hypertrophic cardiomyopathy in an infant with a mitochondrial DNA point mutation (T8993G).

Mutation of mitochondrial (mt) DNA at nucleotide (nt) 8993 has been reported to cause neurogenic weakness, ataxia, retinitis pigmentosa (NARP), or Leigh syndrome (LS). We report a family in whom the mutation was expressed clinically as LS and hypertrophic cardiomyopathy (CMP) in a boy who presented with a history of developmental delay and hypotonia, and who had recurrent lactic acidosis. The mother's first pregnancy resulted in the birth of a stillborn female; an apparently healthy older brother had died suddenly (SIDS) at age 2 months. MtDNA analysis identified the presence of the T8993G point mutation, which was found to be heteroplasmic in the patient's skeletal muscle (90%) and fibroblasts (90%). The identical mutation was present in leukocytes (38%) isolated from the mother, but not from the father or maternal grandmother. Our findings expand the clinical phenotype of the nt 8993 mtDNA mutation to include hypertrophic cardiomyopathy and confirm its cause of LS.

Acidosis, Lactic↗
PubMed1992

Identical point mutations of PMP-22 in Trembler-J mouse and Charcot-Marie-Tooth disease type 1A.

We have investigated the peripheral myelin protein gene, PMP-22, in a family with Charcot-Marie-Tooth disease type 1A (CMT1A). The DNA duplication commonly found in CMT1A was absent in this family, but strong linkage existed between the disease and the CMT1A marker VAW409R3 on chromosome 17p11.2. We found a point mutation in PMP-22 which was completely linked with the disease. The mutation, a proline for leucine substitution in the first putative transmembrane domain, is identical to that recently found in the Trembler-J mouse. The presence of this PMP-22 defect in this CMT1A family and the location of PMP-22 within the DNA duplication associated with CMT1A suggest that both structural alteration and overexpression of PMP-22 may lead to the disease.

Amino Acid Sequence↗
PubMed2002

Point mutations and deletions in the znfn1a1/ikaros gene in chemically induced murine lymphomas.

The Znfn1a1 gene encodes a zinc finger protein called Ikaros, which is criticalfor T-cell development and differentiation. The execution of normal function of Ikaros requires sequence-specific DNA binding, transactivation, and dimerization domains. In this study, exons 3-5 and exon 7 of the Znfn1a1 gene that encode the functional domains of Ikaros were analyzed for point mutations and deletions in murine lymphomas induced by 1,3-butadiene, 2',3'-dideoxycytidine, or phenolphthalein. Missense and frameshift mutations were identified in 11% (11 of 104) of the tumors. Interestingly, 8 of the mutations were identified in the NH2-terminal zinc finger motifs, which are crucial for the DNA-binding function of Ikaros. The other 3 samples carried frameshift mutations in exon 7 that resulted in truncations and abrogation of both transactivation and dimerization domains. One tumor with a missense mutation in the DNA-binding domain also displayed a 45-bp deletion in the dimerization domain. Southern analysis disclosed interstitial homozygous deletions in the functional domains of Ikaros in 4% (3 of 68) of the lymphomas examined. Allelic losses on markers surrounding the Znfn1a1 gene were detected in 27% (12 of 45) of the tumors analyzed. However, only 2 tumors with allelic losses also showed mutations in the Znfn1a1 gene, indicating that other tumor suppressor genes located on this region might be involved as well. Our results suggest inactivation of Ikaros in a subset of chemically induced lymphomas and additionally support the contention of tumor-suppressor activity for Ikaros.

Alleles↗
PubMed1996

K-ras point mutations in endometrial carcinoma: effect on outcome is dependent on age of patient.

Mutations involving the K-ras proto-oncogene are believed to play an important role in the mechanism of tumorigenesis for many human cancers and occur in 10-30% of endometrial carcinomas. In the present study 221 cases of endometrioid endometrial carcinoma obtained from Japanese patients with average follow-up of 41 months were examined for point mutations in codon 12 of K-ras through use of the polymerase chain reaction. In 103 cases lymph node dissection had been performed. K-ras mutations were significantly associated with the presence of lymph node metastases (P < 0.04). Since endometrial carcinoma in premenopausal women generally behaves less aggressively than tumors of similar histologic grade arising in postmenopausal patients, we evaluated the effect of K-ras mutation on outcome in patients stratified into three different age categories (<53 years, premenopausal; 54-59 years, perimenopausal; >60 years, postmenopausal). In the postmenopausal age group (>60 years), the presence of K-ras mutations was statistically significantly associated with patients who died or experienced recurrence (41.2% vs 13.0%; P < 0.03). This was related to a dramatic (greater than eightfold; P = 0.011) increase in the likelihood of adverse outcome between the premenopausal and postmenopausal states for patients whose tumors contained mutant K-ras. These findings point to a possible role for K-ras activation in the mechanism(s) responsible for more aggressive clinical behavior of endometrioid endometrial cancer that is observed in postmenopausal patients.

Adult↗
PubMed1992

Purification and point-mutation analysis of human interleukin-2 (Ser-125).

A new type of IL-2(Ser-125) was purified by semi-preparative RP-HPLC, and its purity was analyzed with microbore HPLC, IEF, SDS-PAGE and capillary electrophoresis (CE). The N-terminal sequencing indicated the microheterogeneity of the N-terminus, i.e., N-Met(2/3) and N-Ala(1/3), which was identified with the results of CE and IEF. The amino acid sequence of the point mutated peptide confirmed the replacement of Cys-125 with Ser.

Amino Acid Sequence↗
PubMed1999

Interferon regulatory factor 1 tryptophan 11 to arginine point mutation abolishes DNA binding.

Interferon regulatory factor-1 (IRF-1) is a transcriptional activator of genes induced by a variety of cytokines and growth factors. Defects in IRF-1 occur frequently in human cancers and may contribute to tumorigenesis. The IRF family of transcription factors share invariant tryptophan residues that have been proposed to function by orienting the DNA contacting residues of IRF-1 with the DNA core sequence of the IRF element. Here we describe a point mutation in IRF-1 that converts the tryptophan at codon 11 to arginine (W11R). The IRF-1 (W11R) mutation abolishes IRF-1 DNA binding and transactivating activities demonstrating the critical role of this invariant tryptophan in IRF-1 function.

Arginine↗
PubMed1997

Mitochondrial dysfunction with myoclonus epilepsy and ragged-red fibers point mutation in nerve, muscle, and adipose tissue of a patient with multiple symmetric lipomatosis.

We report a 64-year-old man presenting with multiple symmetric lipomatosis (MSL) and mitochondrial encephalomyoneuropathy. The diagnosis of a mitochondrial cytopathy was based on the typical clinical symptoms and signs, including chronic progressive external ophthalmoplegia, hearing impairment, cerebellar ataxia, proximal myopathy, and polyneuropathy, and on molecular genetic and histological examinations. As a unique finding, the A-->G(8344) myoclonus epilepsy and ragged-red fibers point mutation was found in peripheral nerve, muscle, and adipose tissue. Muscle biopsy revealed multiple ragged-red fibers and other morphological signs of a mitochondrial myopathy. Sural nerve biopsy demonstrated a mixed axonal and demyelinating neuropathy with extensive loss of myelinated fibers and conspicuous onion bulb formations, as well as structural mitochondrial abnormalities on electron microscopy. These findings clearly demonstrate mitochondrial dysfunction in muscle, adipose tissue, and for the first time also in nervous tissue of an MSL patient, and strongly support the concept of mitochondrial cytopathy as one of the possible causes of multiple symmetric lipomatosis.

Adipose Tissue↗