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At least 577 records · Page 32Linked to original sources
PubMed1994

Lower mutation rate of bovine leukemia virus relative to that of spleen necrosis virus.

Genetic variation of the more complex retroviruses in the human T-cell leukemia virus/bovine leukemia virus (HTLV/BLV) group is less than in some other retroviral genera. To test whether reverse transcription of HTLV/BLV group members is less error prone than that of members of other groups, we developed an assay for detecting forward mutations in BLV, similar to that developed for the simpler spleen necrosis virus (SNV). We used this system to study the rates and types of mutations that occur during a single replication cycle. We found that BLV reverse transcription is approximately two and one-half times less error prone than SNV reverse transcription (4.8 x 10(-6) versus 1.2 x 10(-5) mutation per bp per cycle, respectively). The relative numbers of all types of observed mutations (that is, base pair substitutions, frameshifts, deletions, and deletions with insertions) were similar for BLV and SNV.

Animals↗
PubMed2001

Assessing variability by joint sampling of alignments and mutation rates.

When two sequences are aligned with a single set of alignment parameters, or when mutation parameters are estimated on the basis of a single "optimal" sequence alignment, the variability of both the alignment and the estimated parameters can be seriously underestimated. To obtain a more realistic impression of the actual uncertainty, we propose sampling sequence alignments and mutation parameters simultaneously from their joint posterior distribution given the two original sequences. We illustrate our method with human and orangutan sequences from the hyper variable region I and with gene-pseudogene pairs.

Animals↗
PubMed2005

Low mutational rate of K-ras codon 12 in singular bronchoscopy specimens in suspected lung cancer.

Mutations of the K-ras gene are found in a subset of non-small- cell lung carcinomas (NSCLC). The aim of our study was to determine the K-ras codon 12 mutation in the first, singular bronchoscopy specimen in parallel with the cytological examination for the diagnosis of lung cancer. Samples were obtained by diagnostic bronchoscopy in 140 patients with suspected lung tumors. The analysis of K-ras mutations was carried out by a sensitive two-step mutation- enriched polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. This method has been confirmed earlier to be positive for mutated tumor cells and negative for normal lung parenchyma and bronchus. Of the 140 patients with suspected cancer, 93 were diagnosed as NSCLC by cytology or histology in either the same specimen used for the detection of K-ras mutation or in later biopsies. However, only four K-ras codon 12 mutations were detected in the first bronchoscopic material: one in adenocarcinoma, two in squamous cell tumors, and one mutation was found in a patient with dysplasia which was diagnosed later as a squamous cell carcinoma. Our findings indicate that although the K-ras (codon 12) mutation is a gene lesion infrequently detectable in a singular specimen taken at the first bronchoscopy examination in cases of clinically suspected lung cancer, the detection of this mutation can help to confirm the cytological diagnosis of NSCLC or may be even diagnostic in cytologically negative cases.

Adult↗
PubMed1986

High mutation rate of a spleen necrosis virus-based retrovirus vector.

Spleen necrosis virus (SNV) is an avian retrovirus that efficiently infects some mammalian cells (e.g., dog and rat cells). We constructed an SNV-based vector, which contains less than 1 kilobase (kb) of the retrovirus sequence, and a number of derivatives containing selectable markers. We obtained high-titer virus stocks, over 10(6) transforming units per ml, with a vector whose genomic RNA consists of 1,850 bases (full-length SNV RNA is 7.7 kb). We also studied two vectors that both carry two genes which should be expressed from a single promoter, one gene from unspliced mRNA and the other gene from spliced mRNA. In one vector, both genes were efficiently expressed as expected. However, in the other vector, expression of the gene 3' to the splice acceptor was inhibited. When we selected for expression of the 3' gene is this latter case, we found that the resistant cells contained mutant proviruses in which the 3' gene could be expressed. Furthermore, we found that mutations were generated during a single round of virus replication (provirus to provirus) at a rate of approximately 0.5% mutations per cycle.

Animals↗
PubMed1978

Indirect estimates of mutation rates in tribal Amerindians.

Three different formulations have been used to estimate the average rate/locus/generation with which mutation results in electrophoretically detectable variants of 28 proteins in 12 tribal Amerindian populations. All methods are indirect--i.e., they assume a reasonable approximation to equilibrium between mutation and loss of mutants from the population--and are based on the further assumption that the biochemical traits under consideration are essentially neutral in their phenotypic effects. Despite the fact that the methods draw on somewhat different aspects of the available data, there is satisfactory agreement between them, the average of the three estimates being 1.6 X 10(-5)/locus/generation. This average does not encompass mutation that does not result in a change in electrophoretic mobility or that results in loss of enzyme activity. It is noteworthy that this estimate is in satisfactory agreement with a recent estimate by Neel and Thompson [Neel, J. V. & Thompson, E. A. (1978) Proc. Natl. Acad. Sci. USA 75, 1904--1908] of the mutation pressure necessary to maintain the number of "private" genetic polymorphisms being encountered in Amerindian tribes, if selection is not a factor.

Genetic Variation↗
PubMed2001

Very high mutation rate in offspring of Chernobyl accident liquidators.

Exposure to ionizing radiation has long been suspected to increase mutation load in humans. Nevertheless, such events as atomic bombing seem not to have yielded significant genetic defects. The Chernobyl accident created a different, long-term exposure to radiation. Clean-up teams (or 'liquidators') of the Chernobyl reactor are among those who received the highest doses, presumably in some combination of acute and chronic forms. In this study, children born to liquidator families (currently either in the Ukraine or Israel) conceived after (CA) parental exposure to radiation were screened for the appearance of new fragments using multi-site DNA fingerprinting. Their sibs conceived before (CB) exposure served as critical internal controls, in addition to external controls (non-exposed families). An unexpectedly high (sevenfold) increase in the number of new bands in CA individuals compared with the level seen in controls was recorded. A strong tendency for the number of new bands to decrease with elapsed time between exposure and offspring conception was established for the Ukrainian families. These results indicate that low doses of radiation can induce multiple changes in human germline DNA.

Child↗
PubMed2001

Adrenoleukodystrophy: incidence, new mutation rate, and results of extended family screening.

Utilizing the plasma very long chain fatty acid assay, supplemented by mutation analysis and immunofluorescence assay, we determined the number of X-linked adrenoleukodystrophy (X-ALD) hemizygotes from the United States identified each year in the two laboratories that perform most of the assays in this country: the Kennedy Krieger Institute between 1981 and 1998 and the Mayo Clinic Rochester from 1996 to 1998. The minimum frequency of hemizygotes identified in the United States is estimated to be 1:42,000 and that of hemizygotes plus heterozygotes 1:16,800. Our studies involved 616 pedigrees with a total of 12,787 identified at-risk members. Diagnostic assays were performed in 4,169 at-risk persons (33%) and included members of the extended family. Only 5% of male probands and 1.7% of X-ALD hemizygotes were found to have new mutations. The extended family testing led to the identification of 594 hemizygotes and 1,270 heterozygotes. Two hundred fifty of the newly identified hemizygotes were asymptomatic and represent the group in which therapy has the greatest chance of success. Identification of heterozygotes provides the opportunity for disease prevention through genetic counseling. Diagnostic tests should be offered to all at-risk relatives of X-ALD patients and should include members of the extended family.

Adrenoleukodystrophy↗