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Harman and norharman induce SOS responses and frameshift mutations in bacteria.

Norharman and harman, beta-carboline derivatives with comutagenic activity in Salmonella typhimurium, were examined for their activity to induce SOS responses in S. typhimurium using the umu-test and mutations in Escherichia coli. The inducibility of the umuC gene by norharman and harman was assayed by measuring the levels of beta-galactosidase activity in tester cells harbouring the umuC'-'lacZ fusion gene on a plasmid. In the umu-test, both norharman and harman weakly induced umuC gene expression at 25-100 and 50-150 micrograms/ml, respectively. In the mutation test using reversion from trpE9777 to Trp+, harman was relatively more potent than norharman in inducing the mutations. These results indicate that norharman and harman induce SOS responses as well as reversion of trpE9777 frameshift mutation in bacteria.

Alkaloids↗

New suppressors of frameshift mutations in Salmonella typhimurium.

Several new types of suppressor mutants have been isolated. These were identified among revertants of mutants originally generated by mutagens other than the acridine-derived ICR191. The new suppressors correct mutations other than those with runs of C or G which are recognized by the previously described suppressors. Several frameshift mutations are corrected by more than one suppressor type. Apparently, the DNA base sequence near these mutant sites includes sites of action for several distinct suppressor types.

Base Sequence↗

Insertion of a C in the exon 28 of integrin alphaIIb gene leading to a frameshift mutation is responsible for Glanzmann thrombasthenia in a Japanese case.

BACKGROUND: Glanzmann thrombasthenia (GT) is a hereditary bleeding disorder caused by a qualitative or quantitative defect in the integrin alphaIIbbeta3. OBJECTIVE: Our objective is to identify the gene mutation that resulted in GT. PATIENTS AND METHODS: The patient was a 66-year-old male with a history of frequent bleeding. The expression levels of the integrin proteins in the platelets were determined by flow cytometry and Western blot analysis. The sequences of genomic DNA and mRNA encoding for alphaIIb and beta3 were analyzed by the dye-terminator cycle sequencing method. For transfection experiments, expression vectors encoding for wild-type alphaIIb, mutated alphaIIb, beta3, green fluorescent protein (GFP) fusion wild-type alphaIIb, GFP fusion mutated alphaIIb and DsRed fusion beta3 were constructed. These vectors were transfected to COS-7 cells, and the expression levels were determined. RESULTS: The alphaIIb protein was remarkably reduced in the patient's platelets, and gene analysis showed that the patient possessed compound heterozygous mutations in the alphaIIb gene. One was a C --> G substitution at the splice acceptor site (- 3) of exon 26 (CAG -->GAG) and the other was the insertion of an additional C at the region including six C bases between 2911 and 2916 in exon 28 (InsC). Transfection experiments using COS-7 cells showed that alphaIIb containing InsC had expressed and formed a complex with beta3, but had not been transported to the Golgi apparatus. CONCLUSIONS: In the present study the novel mutation InsC, leading to a frameshift that affects the transmembrane domain and the cytoplasmic tail, was found to be responsible for GT.

Aged↗

A DNA polymerase epsilon mutant that specifically causes +1 frameshift mutations within homonucleotide runs in yeast.

The DNA polymerases delta and epsilon are the major replicative polymerases in the yeast Saccharomyces cerevisiae that possess 3' --> 5' exonuclease proofreading activity. Many errors arising during replication are corrected by these exonuclease activities. We have investigated the contributions of regions of Polepsilon other than the proofreading motifs to replication accuracy. An allele, pol2-C1089Y, was identified in a screen of Polepsilon mutants that in combination with an exonuclease I (exo1) mutation could cause a synergistic increase in mutations within homonucleotide runs. In contrast to other polymerase mutators, this allele specifically results in insertion frameshifts. When pol2-C1089Y was combined with deletions of EXO1 or RAD27 (homologue of human FEN1), mutation rates were increased for +1 frameshifts while there was almost no effect on -1 frameshifts. On the basis of genetic analysis, the pol2-C1089Y mutation did not cause a defect in proofreading. In combination with a deletion of the mismatch repair gene MSH2, the +1 frameshift mutation rate for a short homonucleotide run was increased nearly 100-fold whereas the -1 frameshift rate was unchanged. This suggests that the Pol2-C1089Y protein makes +1 frameshift errors during replication of homonucleotide runs and that these errors can be corrected by either mismatch repair (MMR) or proofreading (in short runs). This is the first report of a +1-specific mutator for homonucleotide runs in vivo. The pol2-C1089Y mutation defines a functionally important residue in Polepsilon.

Alleles↗

A non-radioactive protein truncation test for the sensitive detection of all stop and frameshift mutations.

A new method for mutation detection is described, which is a technical advancement of the protein truncation test. The new technique is non-radioactive and highly sensitive for detection of virtually all sequence mutations, which lead to a stop signal or to the shift of the translation frame. The method includes four steps: 1) capture of the interesting sequence copies out of the sample by binding to an immobilized complementary sequence, 2) PCR amplification of the gene fragment to be analyzed with primers coding both for amino- and carboxy-terminal tags, 3) in vitro transcription and translation, and 4) analysis of the translation products by Western blot. As an evaluation of the new method, we detected mutated gene copies at a dilution of 1 to 40 compared to the non-mutated gene. Using the method, we were able to detect a mutation in the adenomatous polyposis coli tumor suppressor gene (APC) in a stool sample of a colorectal cancer patient. This mutation could not be detected by direct sequencing of the amplified APC gene fragment.

Adenomatous Polyposis Coli↗

A frameshift mutation in the gamma E-crystallin gene of the Elo mouse.

The murine Elo (eye lens obsolescence) mutation confers a dominant phenotype characterized by malformation of the eye lens. The mutation maps to chromosome 1, in close proximity to the gamma E-crystallin gene which is the 3'-most member of the gamma-crystallin gene cluster. We have analysed the sequence of this gene from the Elo mouse and identified a single nucleotide deletion which destroys the fourth and last "Greek key" motif of the protein. This mutation is tightly associated with the phenotype, as no recombination was detected in 274 meioses. In addition, the mutant mRNA is present in the affected lens, providing further support for our hypothesis that the deletion is responsible for the dominant Elo phenotype.

Animals↗

A novel fibrinogen Bbeta chain frameshift mutation in a patient with severe congenital hypofibrinogenaemia.

Congenital afibrinogenemia and severe hypofibrinogenemia are severe bleeding disorders characterized by either undetectable or very low levels of fibrinogen in patients' plasma and platelets. A majority of the reported cases are caused by mutations in the fibrinogen Aalpha chain. In this study, we identified a genetic defect in the fibrinogen Bbeta-chain (FGB) underlying severe hypofibrinogenemia. The propositus frequently displayed bleeding episodes with a prolonged blood-clotting time (thrombin time > 180 s, activated partial thromboplastin time > 300 s, prothrombin time > 120 s) and had a very low level of plasma fibrinogen (1.7-1.8 mg/dl). His parents had a consanguineous marriage, and their functional and immunological fibrinogen was approximately half of the normal level. The platelet fibrinogen level of the propositus could not be detected by western blotting, and his platelet aggregation was severely impaired. DNA screening of the whole fibrinogen gene revealed a homozygous GGGG-->GGG mutation at nucleotide 7,969-7,972 in his FGB gene. The propositus' parents are both heterozygous for this mutation. This mutation contributes to Gly419-->Val, and the 419-434 codons are frame shifted, and a stop codon is formed at codon 435. The predicted truncated Bbeta-chain is 27 amino acids shorter than the normal Bbeta-chain and a central beta-strand in the globular betaC domain is absent, which may lead to destabilization of the entire beta-domain. To the best of our knowledge, this is the first report of such a mutation which is associated with severe hypofibrinogenemia.

Adult↗

NOD2 3020insC frameshift mutation is not associated with inflammatory bowel disease in Chinese patients of Han nationality.

AIM: An insertion mutation at nucleotide 3020 (3020insC) in the Caspase recruitment domain gene (CARD15), originally reported as NOD2, is strongly associated with Crohn's disease. The C-insertion mutation at nucleotide 3020 (3020inC) in the leucine-rich repeat (LRR) region results in a frameshift in the 10(th) LRR followed by a premature stop codon. This truncation mutation is responsible for the inability to activate nuclear factor (NF)-kappaB in response to bacterial lipopolysaccharide (LPS). The present study aimed to genotype NOD2/CARD15 gene 3020insC frameshift mutation in Chinese patients with inflammatory bowel disease. METHODS: We genotyped an insertion polymorphism affecting the leucine-rich region of the protein product by the allele specific PCR in 74 unrelated patients with ulcerative colitis of Han nationality in Hubei Province of China, 15 patients with Crohn's disease and 172 healthy individuals. RESULTS: No significant differences were found in the genotype and allele frequencies of the C-insertion mutation of NOD2 gene among patients with Crohn's disease and ulcerative colitis and healthy controls. CONCLUSION: NOD2 gene 3020insC frameshift mutation is not a major contributor to the susceptibility to both Crohn's disease and ulcerative colitis in Chinese Han patients.

Asian People↗

Antimutagens against spontaneous and induced reversion of a lacZ frameshift mutation in E. coli K-12 strain ND-160.

Isopropyl-beta-D-thiogalactoside (IPTG), at 0.5 or 1.0 mM, is shown to reduce spontaneous, and to virtually abolish caffeine- or quinacrine-induced reversions of the lacZ frameshift mutation in E. coli ND160. Guanosine at 200 micrograms/ml and Co2+ at 15 micrograms/ml had an erratic partial antimutagenic effect on spontaneous lac+ reversions. All 3 agents reduce caffeine-induced (500 micrograms/ml) mutagenesis. Spermine (250 micrograms/ml) also reduces quinacrine-induced Lac+ reversion frequencies in this system.

Caffeine↗

Two frameshift mutations in the RNA-specific adenosine deaminase gene associated with dyschromatosis symmetrica hereditaria.

OBJECTIVE: To report and analyze the mutations of the double-stranded RNA-specific adenosine deaminase (DSRAD) gene in 2 Chinese pedigrees with dyschromatosis symmetrica hereditaria (DSH). DESIGN: Pedigree study. SETTING: Anhui province of China. PATIENTS: Two Chinese families, consisting of 19 individuals (family 1) and 5 individuals (family 2). INTERVENTIONS: We directly performed mutation detection of the DSRAD gene in 2 Chinese families with DSH by sequencing. The whole coding region of DSRAD was amplified by polymerase chain reaction, and products were analyzed by direct sequencing. MAIN OUTCOME MEASURES: Frameshift DSRAD gene mutations. RESULTS: The c.3513insC (Arg1171fs) mutation was found in all patients but not in the healthy individuals from family 1, and the c.3220_3224delGCATC (Gly1073fs) mutation was found in 2 patients but not in the healthy members of family 2. These 2 mutations were not found in 96 unrelated control individuals. CONCLUSION: Our data suggest that these 2 novel frameshift mutations in the DSRAD gene could cause DSH in the Chinese Han population and add new variants to the repertoire of DSRAD mutations in DSH.

Adenosine Deaminase↗

A frameshift mutation in the human fibrinogen Aalpha-chain gene (Aalpha(499)Ala frameshift stop) leading to dysfibrinogen San Giovanni Rotondo.

We have investigated a 53-yr-old asymptomatic white man with decreased functional, but not immunologic, fibrinogen plasma levels together with prolonged thrombin and reptilase times, detected through routine coagulation studies prior to a surgical procedure. A new heterozygous single nucleotide deletion (C) at position Ala499 within the Aalpha-chain gene was identified, which predicted changes of the corresponding amino acids encoded by the subsequent portion of the exon V and the appearance of a premature stop codon at position 518 (Aalpha[499]Ala frameshift stop). The new dysfunctional fibrinogen, San Giovanni Rotondo variant, was confirmed in vivo by SDS-PAGE analysis of HPLC-purified fibrinogen chains. Mass spectrum examination of the abnormal HPLC-purified peak gave an estimated mass (56,088 Da) similar to that predicted by DNA analysis of the mutated Aalpha-chain gene (56,088 Da) and, after tryptic digestion, the truncated Aalpha-chain was shown only in the propositus, who also carried normal Aalpha-chain. In addition, mass spectrum analysis of the tryptic digest of the abnormal chain confirmed the presence of a new and unpaired cysteine at the last position that was predicted to form a disulfide bridge with human serum albumin. Immuno-blot analysis confirmed that fibrinogen San Giovanni Rotondo variant, but not normal fibrinogen. contained substantial amounts of albumin. Present findings confirm that truncated Aalpha-chain lacking part of the terminal domain may be incorporated into mature fibrinogen molecules and normally secreted in the bloodstream.

Afibrinogenemia↗

Somatic frameshift mutations in the MBD4 gene of sporadic colon cancers with mismatch repair deficiency.

Defects of mismatch repair are thought to be responsible for carcinogenesis in hereditary non-polyposis colorectal cancer and about 15% of sporadic colon cancers. The phenotype is seen as microsatellite instability and is known to be caused either by mutations in mismatch repair genes or by aberrant methylation of these genes stabilizing their downregulation. Lack of repair of microsatellite sequence errors, created during replication, leads to a mutation-prone phenotype. Where mutations occur within mononucleotide tracts within exons they cause translation frameshifts, premature cessation of translation and abnormal protein expression. Such mutations have been observed in the TGFbetaRII, BAX, IGFIIR, MSH3 and MSH6 genes in colon and other cancers. We describe here frameshift mutations affecting the gene for the methyl-CpG binding thymine glycosylase, MBD4, in over 40% of microsatellite unstable sporadic colon cancers. The mutations all appear heterozygous but their location would ensure truncation of the protein between the methyl-CpG binding and glycosylase domains, thus potentially generating a dominant negative effect. It is thus possible that such mutations enhance mutation frequency at other sites in these tumours. A suggestion has been made that MBD4 (MED1) mutations may lead to an increased rate of microsatellite instability but this mechanism appears unlikely due to the nature of mutations we have found.

Base Pair Mismatch↗

Evidence for frameshift mutations in the hisH gene of Escherichia coli causing synthesis of a partially active glutamine amidotransferase.

Among eight strains carrying acridine-induced mutations in hisH, five which mapped at four different sites in the promoter-distal region of the gene showed His+ phenotypes on media containing a purine. By complementation analysis, hisH enzyme was shown to be required for growth on purines. Purine-sensitive His+ revertants of strains able to grow on purines carried second-site mutations which in one case could be shown to map in hisG. Strains able to grow on purines were able to grow on 2-thiazolyl-DL-alanine, too. We conclude that frameshift mutations in the promoter-distal part of the hisH gene of E. coli do not completely abolish the activity of the gene product.

Anthranilate Synthase↗

A set of lacZ mutations in Escherichia coli that allow rapid detection of specific frameshift mutations.

We have used site-directed mutagenesis to alter bases in lacZ near the region encoding essential residues in the active site of beta-galactosidase. The altered sequences generate runs of six or seven identical base pairs which create a frameshift, resulting in a Lac- phenotype. Reversion to Lac+ in each strain can occur only by a specific frameshift at these sequences. Monotonous runs of A's (or of T's on the opposite strand) and G's (or C's) have been constructed, as has an alternating -C-G- sequence. These specific frameshift indicator strains complement a set of six previously described strains which detect each of the base substitutions. We have examined a variety of mutagens and mutators for their ability to cause reversion to Lac+. Surprisingly, frameshifts are well stimulated at many of these runs by ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-amino-purine, mutagens not widely known to induce frameshifts. A comparison of ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-aminopurine frameshift specificity with that found with a mutH strain suggests that these mutagens partially or fully saturate or inactivate the methylation-directed mismatch repair system and allow replication errors leading to frameshifts to escape repair. This results in a form of indirect mutagenesis, which can be detected at certain sites.

Base Sequence↗