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At least 487 records · Page 27Linked to original sources
PubMed2004

Novel FLT3 point mutations within exon 14 found in patients with acute myeloid leukaemia.

Internal tandem duplications in FLT3 are the most common mutation in acute myeloid leukaemia (AML), with agarose gel electrophoresis of polymerase chain reaction products (PCR/agarose) being the screening method of choice for these mutations. As PCR/agarose screening does not detect small mutations, single-stranded conformational polymorphism analyses (PCR/SSCP) were used in an attempt to identify previously unrecognized point mutations in FLT3 exons 14 and 15 of 140 AML patients, using newly designed primers that anneal within intron sequences. Novel missense point mutations were found in exon 14, suggesting additional investigations should be performed in AML and other haematopoietic malignancies, using this sensitive technique.

Acute Disease↗
PubMed1990

The molecular genetic analysis of hemophilia A: a directed search strategy for the detection of point mutations in the human factor VIII gene.

A directed-search strategy for point mutations in the factor VIII gene causing hemophilia A was used to screen eight potentially hypermutable CpG dinucleotides occurring at sites deemed to be of functional importance. Polymerase chain reaction-amplified DNA samples from 793 unrelated individuals with hemophilia A were screened by discriminant oligonucleotide hybridization. Point mutations were identified in 16 patients that were consistent with a model of 5-methylcytosine (5mC) deamination. Four new examples of recurrent mutation were demonstrated at the following codons: 336 (CGA----TGA), 372 (CGC----TGC), 372 (CGC----CAC), and 1689 (CGC----TGC). These are functionally important cleavage sites for either activated protein C or thrombin. Further novel C----T transitions were identified in the remaining arginine codons screened (-5, 427, 583, 795, and 1696), resulting in the creation of TGA termination codons. Differences in mutation frequency were found both within and between the CpG sites and between ethnic groups. These differences are assumed to be due to differences in the level of cytosine methylation at these sites, although direct evidence for this inference is lacking.

Base Sequence↗
PubMed2002

A single point mutation within the ED1 gene disrupts correct splicing at two different splice sites and leads to anhidrotic ectodermal dysplasia in cattle.

The ectodysplasin 1 gene ( ED1) encodes a signaling molecule of the tumor necrosis factor family that is involved in fetal development of ectodermal appendages. Mutations in the ED1 gene are responsible for X-linked anhidrotic ectodermal dysplasia characterized by impaired development of hair, teeth, and eccrine sweat glands in human, mouse, and cattle. Two isoforms of ectodysplasin 1, termed ED1-A1 and ED1-A2, arise by alternative splicing and bind to different receptors. We identified a novel ED1 splice site mutation in a cattle family with X-linked anhidrotic ectodermal dysplasia. The point mutation is located within a 5' splice site (splice donor) at the beginning of intron 8 that is used exclusively in the alternatively spliced ED1-A1 transcript. Remarkably, cDNA sequencing demonstrated that both physiological transcripts, i.e., the ED1-A1 and the ED1-A2 splice variant, were affected by this point mutation. In an affected animal, the use of cryptic internal splice donor and acceptor sites within exon 8 lead to the production of a single transcript lacking 51 or 45 bp with respect to the normal ED1-A1 or ED1-A2 transcripts, respectively. The translated protein of the mutated transcript contained a large deletion in the functionally important C-terminal tumor necrosis factor-like domain thus causing the observed phenotype of anhidrotic ectodermal dysplasia. Our findings suggest the presence of a splice enhancer in the ED1 gene in the region of the mutation.

Amino Acid Sequence↗
PubMed1991

c-Ki-ras point mutations in ductectatic-type mucinous cystic neoplasms of the pancreas.

Ductectatic-type mucinous cystic neoplasms of the pancreas constitute a recently recognized new human pancreatic tumor entity. Examination for the presence of point mutations at codon 12 of K-ras by oligonucleotide hybridization in 5 adenomas and 3 carcinomas revealed alteration in 3 and 2, respectively. In 4 of these positive cases, the transition was GGT----GAT (Gly----Asp) with the remaining one, found in a cancer, being GGT----GTT (Gly----Val). In two carcinoma cases, the same point mutation was detected both in the carcinoma area and in a coexisting adenoma component. Thus K-ras point mutation appears to be associated with this particular type of neoplasm in the same manner as observed for typical exocrine pancreas carcinomas. Our study also indicates the possible existence of an adenoma-carcinoma sequence in the evolution of this type of neoplasm and we suggest that K-ras activation may be an important event in the phase of adenoma development.

Adenoma↗
PubMed1993

Novel gyrA point mutation in a strain of Escherichia coli resistant to fluoroquinolones but not to nalidixic acid.

We have previously described a clinical isolate of Escherichia coli (Q2) that is highly resistant to fluoroquinolones (MIC of ciprofloxacin, 16 micrograms/ml) but susceptible to nalidixic acid (MIC of nalidixic acid, 4 micrograms/ml) (N. Moniot-Ville, J. Guibert, N. Moreau, J.F. Acar, E. Collatz, and L. Gutmann, Antimicrob. Agents Chemother. 35:519-523, 1991). Transformation of strain Q2 with a plasmid carrying the wild-type gyrA gene from E. coli K-12(pAFF801) resulted in a 32-fold decrease in the MIC of ciprofloxacin, suggesting that at least one mutation in gyrA was involved in the resistance of Q2. Intragenic gyrA fragments of 668 and 2,500 bp from strain Q2 were amplified by the polymerase chain reaction. We sequenced the 668-bp fragment and identified a single novel point mutation (transition from G to A at position 242), leading to an amino acid substitution (Gly-81 to Asp) in the gyrase A subunit. We constructed hybrid plasmids by substituting either the 668-bp fragment or the 2,500-bp fragment from Q2 DNA, both of which contained the gyrA point mutation, for the corresponding fragments in wild-type gyrA (2,625 bp) of E. coli K-12. When introduced into E. coli KNK453 (gyrA temperature sensitive), both plasmids conferred an eightfold increase in the MIC of ciprofloxacin, but only a twofold increase in the MIC of nalidixic acid. When introduced into E. coli Q2, neither plasmid conferred any change in the MICs of ciprofloxacin or nalidixic acid, suggesting that only the point mutation found in gyrA was involved in the resistance that we observed.

Anti-Infective Agents↗
PubMed1985

An assessment of the importance of error-prone repair and point mutations to forward mutation to L-azetidine-2-carboxylic acid resistance in Escherichia coli.

By comparison of E. coli WP2 with CM891 (uvrA- pKM101) we found that pKM101 plasmid and uvrA- mutation considerably enhanced both spontaneous and chemically-induced reversion at the trp locus. However, little or no increase was observed for forward mutation at the A2C locus. Furthermore, mutation frequency decline was considerably greater for trp reversion than for mutation to A2Cr. Thus neither error-prone repair nor point mutation seemed likely to be the major mechanism for forward mutation at the A2C locus. Results for spontaneous mutation of recA-, polA- and gyrA- strains showed that polA- and gyrA- gave good increases in forward mutation but not in reversion. It was inferred that deletion, transposition and/or larger chromosomal effects rather than point mutation were mainly responsible for most forward mutation.

Azetidinecarboxylic Acid↗
PubMed1993

Point mutation in a family with hyperproinsulinemia detected by single stranded conformational polymorphism.

We previously described a case of familial hyperproinsulinemia, the fifth to be reported. In the present study we characterized the genetic defect carried by this family and demonstrated that it could be detected by polymerase chain reaction-single stranded conformational polymorphism. Since the serum proinsulin molecule from the propositus, a 63-yr-old Japanese man, was eluted on the same fraction of human proinsulin intermediate cleaved only at the B-C junction, we sequenced exon 3 of his insulin gene, including the C-A junction. A point mutation was discovered that changed codon 65 from arginine (CGT) to histidine (CAT) in one allele. This was the same point mutation as that described previously in three unrelated kindreds representing two races, consistent with the hypothesis that the dinucleotide sequence CpG may be a "hot spot" for mutations. Recently, developed polymerase chain reaction-single stranded conformational polymorphism proved useful in detecting this mutation in the family members. The daughter of the propositus and one of his two grandsons were also demonstrated to be heterozygous for this point mutation by this method.

Base Sequence↗
PubMed1996

Ligand-independent activation of fibroblast growth factor receptors by point mutations in the extracellular, transmembrane, and kinase domains.

The fibroblast growth factor receptors (FGFRs) are a family of receptor protein tyrosine kinases that have been shown to mediate a variety of cellular processes including angiogenesis, wound healing, tumorigenesis, and embryonic development. Distinct FGFR mutations in individuals with autosomal dominant disorders of bone growth and development provide a unique opportunity to determine the function of FGFRs during embryonic development. To determine the consequences of these mutations on receptor function, we have made mutations in Xenopus FGFR1 (XFGFR1) and FGFR2 (XFGFR2) that correspond to several of the mutations identified in these dysmorphic syndromes. Analysis of mutant receptor proteins expressed in Xenopus oocytes indicates that all but one have elevated tyrosine kinase activity relative to their wild-type counterparts. Those mutations that give an unpaired cysteine residue in the extracellular domain result in intermolecular disulfide bond formation and covalent receptor dimerization. Microinjection of Xenopus embryos with RNA encoding mutant receptors with elevated tyrosine kinase activity results in ligand-independent induction of mesoderm in animal pole explants. Wild-type XFGFR1 and XFGFR2 do not induce mesoderm when injected at similar doses. Co-injection of RNA encoding a dominant negative FGF receptor, lacking the tyrosine kinase domain, together with RNA encoding various activated FGFRs inhibits mesoderm induction by a receptor activated by a transmembrane domain mutation or extracellular mutations that introduce an unpaired cysteine residue into the extracellular domain but does not inhibit mesoderm induction by receptors bearing a tyrosine kinase domain mutation. These results indicate that different point mutations may activate FGFRs by distinct mechanisms and that ligand-independent FGFR activation may be a feature in common to many skeletal disorders.

Acrocephalosyndactylia↗
PubMed2001

Point mutation in essential genes with loss or mutation of the second allele: relevance to the retention of tumor-specific antigens.

Antigens that are tumor specific yet retained by tumor cells despite tumor progression offer stable and specific targets for immunologic and possibly other therapeutic interventions. Therefore, we have studied two CD4(+) T cell-recognized tumor-specific antigens that were retained during evolution of two ultraviolet-light-induced murine cancers to more aggressive growth. The antigens are ribosomal proteins altered by somatic tumor-specific point mutations, and the progressor (PRO) variants lack the corresponding normal alleles. In the first tumor, 6132A-PRO, the antigen is encoded by a point-mutated L9 ribosomal protein gene. The tumor lacks the normal L9 allele because of an interstitial deletion from chromosome 5. In the second tumor, 6139B-PRO, both alleles of the L26 gene have point mutations, and each encodes a different tumor-specific CD4(+) T cell-recognized antigen. Thus, for both L9 and L26 genes, we observe "two hit" kinetics commonly observed in genes suppressing tumor growth. Indeed, reintroduction of the lost wild-type L9 allele into the 6132A-PRO variant suppressed the growth of the tumor cells in vivo. Since both L9 and L26 encode proteins essential for ribosomal biogenesis, complete loss of the tumor-specific target antigens in the absence of a normal allele would abrogate tumor growth.

Alleles↗
PubMed2003

Absence of point mutation in codons 12 and 13 of K-RAS oncogene in HPV-associated high grade dysplasia and squamous cell cervical carcinoma.

OBJECTIVES: Research data on the K-RAS gene mutation in carcinogenesis of the uterine cervix remain contradictory. Hence the question of whether spot mutations of the RAS genes or their excessive expression are an indispensable condition for the generation of the neoplastic phenotype of the cervical epithelial cell remains without an explicit answer. AIM OF THE STUDY: The purpose of the study was identification of point mutation in codons 12 and 13 of the first exon of K-RAS gene in DNA from squamous cell cervical carcinomas, high grade dysplasias, and normal epithelium. MATERIAL AND METHODS: The study group consisted of 35 postoperative tissues from patients diagnosed with high grade dysplasia and 29 postoperative tissues from patients diagnosed with squamous cell cervical carcinoma. The control group consisted of normal cervical tissue specimens obtained from 33 patients who underwent hysterectomy due to uterine leiomyomas. Identification of point mutation in codons 12 and 13 of the first exon of K-RAS genes was performed using polymerase chain reaction (PCR)-SSCP technique. RESULTS: PCR-SSCP analysis did not reveal the presence of point mutation in codons 12 and 13 of K-RAS gene in any of the analyzed cases.

Adult↗
PubMed1998

Different point mutations within the conserved N-glycosylation motif of pseudorabies virus glycoprotein M result in expression of a nonglycosylated form of the protein.

Glycoprotein M (gM) constitutes one of the rare examples of a nonessential glycoprotein conserved throughout all herpesvirus subfamilies. Whereas gM in wild-type pseudorabies virus (PrV) strains carries an N-glycan, gM of the attenuated strain Bartha is not glycosylated due to a point mutation in the N-glycosylation motif. Since PrV Bartha lacks glycoproteins E and I and carries a mutated gC, we analysed glycosylation of gM in isogenic PrV glycoprotein deletion mutants. Whereas gM was glycosylated normally in most mutants, two independent gC deletion mutants and a gI mutant expressed a nonglycosylated form of gM. DNA sequence analyses revealed the presence of point mutations in the N-glycosylation consensus motif. Surprisingly, mutations in strain Bartha, the two gC-deletion mutants and the gI mutant proved to be different, although all affected the N-glycosylation motif. Thus, our data show that different, apparently independent point mutations cause expression of nonglycosylated gM.

Amino Acid Sequence↗
PubMed2001

Point mutations in the murine fumarylacetoacetate hydrolase gene: Animal models for the human genetic disorder hereditary tyrosinemia type 1.

Hereditary tyrosinemia type 1 (HT1) is a severe autosomal recessive metabolic disease associated with point mutations in the human fumarylacetoacetate hydrolase (FAH) gene that disrupt tyrosine catabolism. An acute form of HT1 results in death during the first months of life because of hepatic failure, whereas a chronic form leads to gradual development of liver disease often accompanied by renal dysfunction, childhood rickets, neurological crisis, and hepatocellular carcinoma. Mice homozygous for certain chromosome 7 deletions of the albino Tyr; c locus that also include Fah die perinatally as a result of liver dysfunction and exhibit a complex syndrome characterized by structural abnormalities and alterations in gene expression in the liver and kidney. Here we report that two independent, postnatally lethal mutations induced by N-ethyl-N-nitrosourea and mapped near Tyr are alleles of Fah. The Fah(6287SB) allele is a missense mutation in exon 6, and Fah(5961SB) is a splice mutation causing loss of exon 7, a subsequent frameshift in the resulting mRNA, and a severe reduction of Fah mRNA levels. Increased levels of the diagnostic metabolite succinylacetone in the urine of the Fah(6287SB) and Fah(5961SB) mutants indicate that these mutations cause a decrease in Fah enzymatic activity. Thus, the neonatal phenotype present in both mutants is due to a deficiency in Fah caused by a point mutation, and we propose Fah(5961SB) and Fah(6287SB) as mouse models for acute and chronic forms of human HT1, respectively.

Acute Disease↗
PubMed1997

CMO I deficiency caused by a point mutation in exon 8 of the human CYP11B2 gene encoding steroid 18-hydroxylase (P450C18).

Corticosterone methyloxidase I (CMO I) deficiency is an autosomal recessive disorder of aldosterone biosynthesis. To determine further the molecular genetic basis of CMO I deficiency, a patient of Turkish origin that suffered from CMO I deficiency was studied. Nucleotide sequencing of the PCR-amplified exons from the genomic DNA of this patient revealed a single point mutation CTG (leucine) CCG (proline) at codon 461 in exon 8 of CYP11B2, which is involved in the putative heme binding site of steroid 18-hydroxylase (P450(C18)). The expression study using a cDNA introducing the point mutation revealed that the amino acid substitution totally abolishes the P450(C18)p3 enzyme activities required for conversion of 11-deoxycorticosterone to aldosterone, even though the mutant product was detected in the mitochondrial fraction of the transfected cells. These results suggest that this point mutation causes CMO I deficiency.

Aldosterone↗
PubMed1997

Point mutations in human GLI3 cause Greig syndrome.

Greig cephalopolysyndactyly syndrome (GCPS, MIM 175700) is a rare autosomal dominant developmental disorder characterized by craniofacial abnormalities and post-axial and pre-axial polydactyly as well as syndactyly of hands and feet. Human GLI3, located on chromosome 7p13, is a candidate gene for the syndrome because it is interrupted by translocation breakpoints associated with GCPS. Since hemizygosity of 7p13 resulting in complete loss of one copy of GLI3 causes GCPS as well, haploinsufficiency of this gene was implicated as a mechanism to cause this developmental malformation. To determine if point mutations within GLI3 could be responsible for GCPS we describe the genomic sequences at the boundaries of the 15 exons and primer pair sequences for mutation analysis with polymerase chain reaction-based assays of the entire GLI3 coding sequences. In two GCPS cases, both of which did not exhibit obvious cytogenetic rearrangements, point mutations were identified in different domains of the protein, showing for the first time that Greig syndrome can be caused by GLI3 point mutations. In one case a nonsense mutation in exon X generates a stop codon truncating the protein in the C-H link of the first zinc finger. In the second case a missense mutation in exon XIV causes a Pro-->Ser replacement at a position that is conserved among GLI genes from several species altering a potential phosphorylation site.

Abnormalities, Multiple↗
PubMed2004

PCR-based detection of minority point mutations.

The need for detection of minority mutations (i.e., a few mutants within a high excess of wild-type alleles) arises frequently in the field of cancer and molecular genetics. Current mutation detection technologies are limited by several technical factors when it comes to the detection of minority point mutations, including generation of misincorporations by the DNA polymerase during PCR amplification. Primer ligation-mediated PCR methodologies for detection of mutations in an excess wild-type sequences are described, that can be applied for detection of both known and unknown minority point mutations. Furthermore, a new methodology is described, hairpin-PCR, which has the potential to completely eliminate PCR errors from amplified sequences, prior to minority mutation detection. Combination of these technologies can effectively tackle the problem of minority mutation detection, in order to pursue demanding applications such as identification of cancer cells at an early stage, detection of mutations in single cells, identification of minimal residual disease, or investigation of mechanisms of spontaneous mutagenesis.

DNA Mutational Analysis↗
PubMed1991

Point mutations upstream of the yeast ADH2 poly(A) site significantly reduce the efficiency of 3'-end formation.

The sequences directing formation of mRNA 3' ends in Saccharomyces cerevisiae are not well defined. This is in contrast to the situation in higher eukaryotes in which the sequence AAUAAA is known to be crucial to proper 3'-end formation. The AAUAAA hexanucleotide is found upstream of the poly(A) site in some but not all yeast genes. One of these is the gene coding for alcohol dehydrogenase, ADH2. Deletion or a double point mutation of the AAUAAA has only a small effect on the efficiency of the reaction, and in contrast to the mammalian system, it is most likely not operating as a major processing signal in the yeast cell. However, we isolated point mutations which reveal that a region located approximately 80 nucleotides upstream of the poly(A) site plays a critical role in either transcription termination, polyadenylation, or both. These mutations represent the first point mutations in yeasts which significantly reduce the efficiency of 3'-end formation.

Alcohol Dehydrogenase↗
PubMed2004

Altering a gene involved in nuclear distribution increases the repeat-induced point mutation process in the fungus Podospora anserina.

Repeat-induced point mutation (RIP) is a homology-dependent gene-silencing mechanism that introduces C:G-to-T:A transitions in duplicated DNA segments. Cis-duplicated sequences can also be affected by another mechanism called premeiotic recombination (PR). Both are active over the sexual cycle of some filamentous fungi, e.g., Neurospora crassa and Podospora anserina. During the sexual cycle, several developmental steps require precise nuclear movement and positioning, but connections between RIP, PR, and nuclear distributions have not yet been established. Previous work has led to the isolation of ami1, the P. anserina ortholog of the Aspergillus nidulans apsA gene, which is required for nuclear positioning. We show here that ami1 is involved in nuclear distribution during the sexual cycle and that alteration of ami1 delays the fruiting-body development. We also demonstrate that ami1 alteration affects loss of transgene functions during the sexual cycle. Genetically linked multiple copies of transgenes are affected by RIP and PR much more frequently in an ami1 mutant cross than in a wild-type cross. Our results suggest that the developmental slowdown of the ami1 mutant during the period of RIP and PR increases time exposure to the duplication detection system and thus increases the frequency of RIP and PR.

Cell Nucleus↗
PubMed2005

In vivo activity of gemifloxacin, moxifloxacin and levofloxacin against pneumococci with gyrA and parC point mutations in a sepsis mouse model measured with the all or nothing mortality end-point.

A dose-decreasing immunocompetent sepsis mouse model was used to evaluate the in vivo effect of levofloxacin, moxifloxacin and gemifloxacin, using a ciprofloxacin/levofloxacin susceptible serotype 6B strain (ciprofloxacin MIC: 1 mg/l) and two resistant serotype 14 and 19F strains with gyrA and parC point mutations (ciprofloxacin MICs of 32 and 64 mg/l, respectively). Significant higher in vivo activity was found for moxifloxacin and gemifloxacin than for levofloxacin against strains 1 and 2, and for gemifloxacin versus moxifloxacin or levofloxacin against strain 3. Gemifloxacin treatment resulted in 100% survival against strains 1 and 2(AUC0-24 h/MIC of 30 and 62) but against strain 3, survival was 60-80% (AUC0-24 h/MIC of 93). Similar AUC0-24 h/MIC values produced different therapeutic results suggesting that in vitro parameters other than the MIC could influence efficacy predictions based on in vitro susceptibility tests (MICs) or pharmacodynamic parameters (AUC0-24 h/MIC).

Animals↗