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Correction of frameshift mutations with single-stranded and double-stranded DNA fragments prepared from phagemid/plasmid DNAs.

We recently found that a heat-denatured, double-stranded DNA fragment, prepared from plasmid DNA (dsHES), and a sense single-stranded DNA fragment, prepared from single-stranded phagemid DNA (fSense), corrected an inactivated hygromycin-resistance and enhanced green fluorescence protein fusion (Hyg-EGFP) gene containing a base substitution (G:C to C:G) mutation 2-fold and more than 10-fold, respectively, more efficiently than the conventional PCR fragment (pcrHES), in the small fragment homologous replacement method. In this study, we tested the abilities of these new DNA fragments to correct Hyg-EGFP genes inactivated by one base insertion (+G) and deletion (-C) mutations. In contrast to its activity with the substitution mutation, the fSense fragment showed similar efficiencies to those of the dsHES fragment in the correction of frameshift mutations. For the correction of the insertion mutation, the efficiencies were in the order of dsHES (0.21%)>or=fSense (0.18%)>pcrHES (0.08%). In the case of the correction of the deletion mutation, the efficiencies were in the order of fSense (0.27%)>or=dsHES (0.19%)>pcrHES (0.12%). These results suggest that sense single- and double-stranded DNA fragments prepared from phagemid and plasmid DNAs, respectively, have the potential to correct frameshift mutations.

Animals↗

Mechanisms of spontaneous and induced frameshift mutation in bacteriophage T4.

Frequencies of spontaneous and proflavine-induced frameshift mutations increased dramatically as a function of the number of reiterated base pairs at each of two sites in the lysozyme gene of bacteriophage T4. At each site, proflavine induces addition mutations more frequently than deletion mutations. We confirm that the steroidal diamine, irehdiamine A, induces frameshift addition mutations. At sites of reiterated bases, we propose that base pairing is misaligned adjacent to a gap. The misaligned configuration is stabilized by the stacking of mutagen molecules around the extrahelical base, forming a sandwich. Proflavine induces addition mutations efficiently at a site without any reiterated bases. Mutagenesis at such sites may be due to mutagen-induced stuttering of the replication complex.

Base Sequence↗

Frameshift mutation in the collagen VI gene causes Ullrich's disease.

Patients with Ullrich's disease have generalized muscle weakness, multiple contractures of the proximal joints, and hyperextensibility of the distal joints. Recently, we found a deficiency of collagen VI protein in two patients with Ullrich's disease. In this study, we detected a homozygous 26 bp deletion in exon 14 of the collagen VI alpha 2 gene (COL6A2) in one patient. This mutation causes a frameshift and a premature termination codon, and results in a truncated collagen VI alpha 2 chain. Our data suggest that at least some cases of Ullrich's disease result from recessive mutations in COL6A2.

Adult↗

First description of a frameshift mutation in the alpha1-globin gene associated with alpha-thalassaemia.

A frameshift mutation in the alpha1-globin gene, responsible for a clinically mild alpha-thalassaemia phenotype, has been characterized in a Spanish woman. After excluding the most common forms of alpha-thalassaemia found in the Mediterranean area, both alpha-globin genes (alpha1 and alpha2) were amplified and analysed selectively by non-radioactive single-strand conformation polymorphism (SSCP). An abnormal SSCP mobility was present in the second exon of the alpha1-globin gene and direct sequence analysis revealed a 13 bp deletion (between codons 51 and 55) affecting a single allele. The consequence of this mutation is a reading frameshift leading to a novel amino acid coding sequence from codons 51-61 and a premature stop signal at new position 62, which results in a net reduction of the affected alpha-globin chain output. The presence of this new mutation was confirmed by restriction enzyme analysis of the specific PCR product.

Aged↗

Identification of a frameshift mutation responsible for the silent phenotype of human serum cholinesterase, Gly 117 (GGT----GGAG).

A frameshift mutation that causes a silent phenotype for human serum cholinesterase was identified in the DNA of seven individuals of two unrelated families. The mutation, identified using the polymerase chain reaction, causes a shift in the reading frame from Gly 117, where GGT (Gly)----GGAG (Gly+ 1 base) to a new stop codon created at position 129. This alteration is upstream of the active site (Ser 198), and, if any protein were made, it would represent only 22% of the mature enzyme found in normal serum. Results of analysis of the enzymatic activities in serum agreed with the genotypes inferred from the nucleotide sequence. Rocket immunoelectrophoresis using alpha-naphthyl acetate to detect enzymatic activity showed an absence of cross-reactive material, as expected. One additional individual with a silent phenotype did not show the same frameshift mutation. This was not unexpected, since there must be considerable molecular heterogeneity involved in causes for the silent cholinesterase phenotype. This is the first report of a molecular mechanism underlying the silent phenotype for serum cholinesterase. The analytical approach used was similar to the one we recently employed to identify the mutation that causes the atypical cholinesterase variant.

Amino Acid Sequence↗

A new model for phenotypic suppression of frameshift mutations by mutant tRNAs.

According to the prevailing model, frameshift-suppressing tRNAs with an extra nucleotide in the anticodon loop suppress +1 frameshift mutations by recognizing a four-base codon and promoting quadruplet translocation. We present three sets of experiments that suggest a general alternative to this model. First, base modification should actually block such a four-base interaction by two classical frameshift suppressors. Second, for one Salmonella suppressor tRNA, it is not mutant tRNA but a structurally normal near cognate that causes the +1 shift in-frame. Finally, frameshifting occurs in competition with normal decoding of the next in-frame codon, consistent with an event that occurs in the ribosomal P site after the translocation step. These results suggest an alternative model involving peptidyl-tRNA slippage at the classical CCC-N and GGG-N frameshift suppression sites.

Anticodon↗

Frameshift mutations induced by an Escherichia coli strain carrying a mutator gene, mutD5.

We have studied eight frameshift mutations induced by the Escherichia coli mutator allele mutD5 in a derivative of the bacteriophage M13mp8, carrying an insertion of 91 base pairs derived from the tetR gene of pBR 322. All mutations were analyzed by the dideoxy sequencing method and were found to be deletions of a GC base pair which occurred in regions characterized by the presence of at least two GC base pairs. We have attempted to explain these results by the looping-out model, which was previously proposed to unify the results obtained with mutD5.

Base Sequence↗

A new compound heterozygous frameshift mutation in the type II 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) gene causes salt-wasting 3 beta-HSD deficiency congenital adrenal hyperplasia.

We report a new compound heterozygous frameshift mutation in the type II 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) gene in a Pakistanian female child with the salt-wasting form of 3 beta-HSD deficiency congenital adrenal hyperplasia. The child, born with clitoral enlargement, manifesting salt-wasting adrenal crisis, and public hair growth during infancy, was treated with hormonal replacement therapy. The etiology of her congenital adrenal hyperplasia, however, was not defined. Two of her siblings, as well as one paternal cousin with ambiguous genitalia and palpable gonads and another paternal cousin with normal female genitalia, had symptoms of adrenal crisis and died during early infancy. Thus, although the family history suggested possible 3 beta-HSD deficiency disorder, suppressed adrenal function caused by excess glucocorticoid therapy in this child at 7 yr of age did not allow hormonal diagnosis. To confirm 3 beta-HSD deficiency, we sequenced the type II 3 beta-HSD gene in the patient, her family, and the parents of her decreased paternal cousins. The type II 3 beta-HSD gene region of a putative promoter, exons I, II, III, and IV, and exon-intron boundaries were amplified by PCR and sequenced in all subjects. The DNA sequence of the child revealed a single nucleotide deletion at codon 318 [ACA (Thr)-->AA] in exon IV in one allele, and two nucleotide deletions at codon 273 [AAA(Lys)-->A] in exon IV in the other allele. The remaining gene sequences were normal. The codon 318 mutation was found in one allele from the father, brother, and parents of the deceased paternal cousins. The codon 273 mutation was found in one allele of the mother and a sister. These findings confirmed inherited 3 beta-HSD deficiency in the child caused by the compound heterozygous type II 3 beta-HSD gene mutation. Both codon 273 and 318 mutations yielding frameshift and premature stop codons at codons 279 and 367, respectively, are predicted to result in an altered and truncated type II 3 beta-HSD protein, thereby causing salt-wasting 3 beta-HSD deficiency in the patient. The type II 3 beta-HSD gene findings and clinical history of her family members suggest that the patient's deceased siblings were likely affected males with the same compound heterozygous mutations of the gene as in the proband, whereas the deceased cousins were likely affected with the homozygous codon 318 mutation in the gene.

3-Hydroxysteroid Dehydrogenases↗

[Suppression of frameshift mutation as a result of partial inactivation of translation termination factors in Saccharomyces cerevisiae yeast].

Special search for frameshift mutations, which are suppressed by the cytoplasmic [PSI] factor and by omnipotent nonsense suppressors (recessive mutations in the SUP35 and SUP45 genes), partially inactivating a translation termination complex, was initiated in the LYS2 gene in the yeast Saccharomyces cerevisiae. Mutations were obtained after exposure to UV light and treatment with a mixture consisting of 1.6- and 1.8-dinitropyrene (DNP). This mixture was shown to induce mutations of the frameshift type with a high frequency. The majority of these mutations were insertions of one A or T, which is in good agreement with the data obtained in studies of DNP-induced mutagenesis in other eukaryotes. Frameshift suppression in yeast was first shown on the example of the mutation obtained in this work (lys2-90), which carried the insertion of an extra T in the sequence of five T. This frameshift suppression was shown to occur in the presence of the [PSI] factor (i.e., due to the prion form of the translation release factor eRF3) and as a result of mutations in genes SUP35 or SUP45, which partially inactivate translation termination factors eRF3 and eRF1, respectively. Alternative mechanisms of programmed translational frameshifting in the course of translation and the possibility of enhancing the effectiveness of such frameshifting in the presence of the [PSI] factor are considered.

Base Sequence↗

Effect of frameshift mutation in the pre-C region of hepatitis B virus on the X and C genes.

We have previously cloned a mutant hepatitis B virus (HBV) genome which had one thymidine addition in the pre-C region resulting in a frameshift mutation in the pre-C region and fusion of the X and C genes. We constructed plasmids containing serially deleted and/or back-mutated (authentic) pre-C regions to study the effect of the frameshift mutation. COS cells transfected with plasmids containing the frameshifted pre-C region produced a 21K C protein (P21c) but not a 22K partially processed pre-C protein (P22). On the other hand, COS cells transfected with plasmids containing the back-mutated pre-C region produced P22. This result was also observed in HepG2-K8 cells producing the mutant HBV particles. Therefore, the pre-C region of HBV is likely to be non-essential for virus replication. COS cells transfected with the plasmid containing a fused X-C open reading frame (ORF) produced a 40K X-C fusion protein. This X-C fusion protein exerted transcriptional trans-activation. These results suggest that the mutant HBV has a C gene with a defective pre-C region and a fused X-C ORF, and hence cannot synthesize 16K HBeAg (P16e).

Amino Acid Sequence↗

Epidermolytic hyperkeratosis and epidermolysis bullosa simplex caused by frameshift mutations altering the v2 tail domains of keratin 1 and keratin 5.

The cytoskeleton of epithelial cells is formed by heteropolymeric keratin proteins characterized by a central alpha-helical rod flanked by nonhelical head and tail domains of variable sequence. Most mutations described in 18 distinct keratins disrupt highly conserved regions at the boundaries of the rod, which have been recognized as zones of overlap during keratin alignment and assembly into intermediate filaments. We recently reported the first mutation located in a keratin tail domain (V2) in ichthyosis hystrix Curth-Macklin. In this study, we report two novel frameshift mutations that are predicted to alter the tail of keratin 1 or keratin 5, leading to an atypical form of epidermolytic hyperkeratosis and a mild form of epidermolysis bullosa simplex, respectively. Mutation analysis of the patient with epidermolytic hyperkeratosis revealed a de novo heterozygous nucleotide insertion (1752insG) in exon 9 of KRT1, predicted to result in an aberrant 69 residue keratin 1 tail. In the patient with mild epidermolysis bullosa simplex, we identified a single nucleotide deletion (1635delG) in exon 9 of KRT5 leading to frameshift and translation of an abnormal V2 domain, 35 amino acids longer than the native keratin 5 tail. Our results, together with previous observations, establish the existence of a subgroup of keratin disorders due to frameshift mutations altering the keratin tail domains that are characterized by phenotypic heterogeneity.

Adolescent↗

The diabetes-prone BB rat carries a frameshift mutation in Ian4, a positional candidate of Iddm1.

Diabetes-prone (DP) BB rats spontaneously develop insulin-dependent diabetes resembling human type 1 diabetes. They also exhibit lifelong T-cell lymphopenia. Functional and genetic data support the hypothesis that the gene responsible for the lymphopenia, Lyp, is also a diabetes susceptibility gene, named Iddm1. We constructed a 550-kb P1-derived artificial chromosome contig of the region. Here, we present a corrected genetic map reducing the genetic interval to 0.2 cM and the physical interval to 150-290 kb. A total of 13 genes and six GenomeScan models are assigned to the homologous human DNA segment on HSA7q36.1, 8 of which belong to the family of immune-associated nucleotides (Ian genes). Two of these are orthologous to mouse Ian1 and -4, both excellent candidates for Iddm1. In normal rats, they are expressed in the thymus and T-cell regions of the spleen. In the thymus of lymphopenic rats, Ian1 exhibits wild-type expression patterns, whereas Ian4 expression is reduced. Mutational screening of their coding sequences revealed a frameshift mutation in Ian4 among lymphopenic rats. The mutation results in a truncated protein in which the COOH-terminal 215 amino acids-including the anchor localizing the protein to the outer mitochondrial membrane-are replaced by 19 other amino acids. We propose that Ian4 is identical to Iddm1.

Amino Acid Sequence↗

Photoreactivation reverses ultraviolet radiation induced premutagenic lesions leading to frameshift mutations in Escherichia coli.

The effect of photoreactivation of the ultraviolet radiation induced reversion of a trpE9777 frameshift mutation was studied in a uvr A6 derivative of Escherichia coli K12. Two different photoreactivation treatments were used, one providing a single flash of photoreactivating light and another providing 10 min of light from fluorescent lamps. The reversion frequency of the trpE9777 frameshift mutation was strongly reduced when subsequently exposed to visible light. The dose modification factor (the ratio of equally effective doses), for cells challenged with single-flash photoreactivation, for survival and induction of reversion to Trp+ was 3.6 and 3.4, respectively. UV induction of RecA protein synthesis was not reversed by a single flash of photoreactivation. The dose modification factor for 10 min of fluorescent lamp photoreactivation for survival and for induction of reversion to Trp+ was 6.5 and 6.3, respectively. The dose modification factor for 10 min of photoreactivation for induction of RecA protein was 1.7-2.5. Photoreactivation decreased the reversion of trpE9777 and increased survival to the same extent. We concluded that cyclobutyl pyrimidine dimers are the premutagenic lesions of UV mutagenesis of the trpE9777 allele in a uvr A6 background.

Dose-Response Relationship, Radiation↗

Missense and nonsense suppressors can correct frameshift mutations.

Missense and nonsense suppressor tRNAs, selected for their ability to read a new triplet codon, were observed to suppress one or more frameshift mutations in trpA of Escherichia coli. Two of the suppressible frameshift mutants, trpA8 and trpA46AspPR3, were cloned, sequenced, and found to be of the +1 type, resulting from the insertion of four nucleotides and one nucleotide, respectively. Twenty-two suppressor tRNAs were examined, 20 derived from one of the 3 glycine isoacceptor species, one from lysT, and one from trpT. The sequences of all but four of the mutant tRNAs are known, and two of those four were converted to suppressor tRNAs that were subsequently sequenced. Consideration of the coding specificities and anticodon sequences of the suppressor tRNAs does not suggest a unitary mechanism of frameshift suppression. Rather, the results indicate that different suppressors may shift frame according to different mechanisms. Examination of the suppression windows of the suppressible frameshift mutations indicates that some of the suppressors may work at cognate codons, either in the 0 frame or in the +1 frame, and others may act at noncognate codons (in either frame) by some as-yet-unspecified mechanism. Whatever the mechanisms, it is clear that some +1 frameshifting can occur at non-monotonous sequences. A striking example of a frameshifting missense suppressor is a mutant lysine tRNA that differs from wild-type lysine tRNA by only a single base in the amino acid acceptor stem, a C to U70 transition that results in a G.U base pair. It is suggested that when this mutant lysine tRNA reads its cognate codon, AAA, the presence of the G.U base pair sometimes leads either to a conformational change in the tRNA or to an altered interaction with some component of the translation machinery involved in translocation, resulting in a shift of reading frame. In general, the results indicate that translocation is not simply a function of anticodon loop size, that different frameshifting mechanisms may operate with different tRNAs, and that conformational features, some far removed from the anticodon region, are involved in maintaining fidelity in translocation.

Amino Acid Sequence↗

Frameshift mutations in the MBD4/MED1 gene in primary gastric cancer with high-frequency microsatellite instability.

MBD4/MED1 is a newly identified mismatch repair gene, which is mutated in colon, endometrial, and pancreatic high-frequency microsatellite instability (MSI-H) tumors. To assess its role in gastric cancers, we investigated MBD4/MED1 mutations in sporadic gastric cancers, compared with colon cancers. Frameshift mutations were found in 29% of gastric and 20% of colon MSI-H cancers, but not in any low-frequency microsatellite instability/microsatellite stable cancers. MBD4/MED1 is mutated in gastric cancers as frequently as in colon cancers; these mutations reduce the accuracy of DNA repair, and may lead to cancer progression.

Aged↗

Establishment of a human induced pluripotent stem cell line, KMUGMCi011-A, from a patient bearing a frameshift mutation in the KMT2D gene leading Kabuki syndrome 1.

Kabuki syndrome 1 is a rare genetic disorder typically characterized by facial abnormalities, cognitive impairment, developmental delay and organ dysfunction. It is caused by a loss-of-function mutation in the KMT2D gene. The peripheral blood mononuclear cells from a patient carrying frameshift mutation in the KMT2D gene were reprogrammed using the CytoTune-iPS2.0 Sendai Reprogramming Kit. This frameshift mutation results in a truncated protein. This established human induced pluripotent cell line will allow proper in vitro disease modelling of Kabuki syndrome 1.

Journal Article↗

A novel frameshift mutation of the mtDNA COIII gene leads to impaired assembly of cytochrome c oxidase in a patient affected by Leigh-like syndrome.

We report on a novel frameshift mutation in the mtDNA gene encoding cytochrome c oxidase (COX) subunit III. The proband is an 11-year-old girl with a negative family history and an apparently healthy younger brother. Since 4 years of age, she has developed a progressive spastic paraparesis associated with ophthalmoparesis and moderate mental retardation. The presence of severe lactic acidosis and Leigh-like lesions of putamina prompted us to perform muscle and skin biopsies. In both, a profound, isolated defect of COX was found by histochemical and biochemical assays. Sequence analysis of muscle mtDNA resulted in the identification of a virtually homoplasmic frameshift mutation in the COIII gene, due to the insertion of an extra C at nucleotide position 9537 of mtDNA. Although the 9537C(ins) does not impair transcription of COIII, no full-length COX III protein was detected in mtDNA translation assays in vivo. Western blot analysis of two-dimensional blue-native electrophoresis showed a reduction of specific crossreacting material and the accumulation of early-assembly intermediates of COX, whereas the fully assembled complex was absent. One of these intermediates had an electrophoretic mobility different from those seen in controls, suggesting the presence of a qualitative abnormality of COX assembly. Immunostaining with specific antibodies failed to detect the presence of several smaller subunits in the complex lacking COX III, in spite of the demonstration that these subunits were present in the crude mitochondrial fraction of patient's cultured fibroblasts. Taken together, the data indicate a role for COX III in the incorporation and maintenance of smaller COX subunits within the complex.

Base Sequence↗

Somatic frameshift mutations in the BAX gene in colon cancers of the microsatellite mutator phenotype.

Cancers of the microsatellite mutator phenotype (MMP) show exaggerated genomic instability at simple repeat sequences. More than 50 percent (21 out of 41) of human MMP+ colon adenocarcinomas examined were found to have frameshift mutations in a tract of eight deoxyguanosines [(G)8] within BAX, a gene that promotes apoptosis. These mutations were absent in MMP- tumors and were significantly less frequent in (G)8 repeats from other genes. Frameshift mutations were present in both BAX alleles in some MMP+ colon tumor cell lines and in primary tumors. These results suggest that inactivating BAX mutations are selected for during the progression of colorectal MMP+ tumors and that the wild-type BAX gene plays a suppressor role in a p53-independent pathway for colorectal carcinogenesis.

Adenocarcinoma↗