Instability of CAG and CTG trinucleotide repeats in Saccharomyces cerevisiae.

A quantitative genetic assay was developed to monitor alterations in tract lengths of trinucleotide repeat sequences in Saccharomyces cerevisiae. Insertion of (CAG)50 or (CTG)50 repeats into a promoter that drives expression of the reporter gene ADE8 results in loss of expression and white colony color. Contractions within the trinucleotide sequences to repeat lengths of 8 to 38 restore functional expression of the reporter, leading to red colony color. Reporter constructs including (CAG)50 or (CTG)50 repeat sequences were integrated into the yeast genome, and the rate of red colony formation was measured. Both orientations yielded high rates of instability (4 x 10(-4) to 18 x 10(-4) per cell generation). Instability depended on repeat sequences, as a control harboring a randomized (C,A,G)50 sequence was at least 100-fold more stable. PCR analysis of the trinucleotide repeat region indicated an excellent correlation between change in color phenotype and reduction in length of the repeat tracts. No preferential product sizes were observed. Strains containing disruptions of the mismatch repair gene MSH2, MSH3, or PMS1 or the recombination gene RAD52 showed little or no difference in rates of instability or distributions of products, suggesting that neither mismatch repair nor recombination plays an important role in large contractions of trinucleotide repeats in yeast.

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Nucleotide sequence of the Streptococcus pneumoniae hexB mismatch repair gene: homology of HexB to MutL of Salmonella typhimurium and to PMS1 of Saccharomyces cerevisiae.

Journal of Bacteriology ◽

10.1128/jb.171.10.5332-5338.1989 ◽

1989 ◽

Vol 171 (10) ◽

pp. 5332-5338 ◽

Cited By ~ 29

Author(s):

M Prudhomme ◽

B Martin ◽

V Mejean ◽

J P Claverys

Keyword(s):

Saccharomyces Cerevisiae ◽

Streptococcus Pneumoniae ◽

Nucleotide Sequence ◽

Salmonella Typhimurium ◽

Mismatch Repair ◽

Mismatch Repair Gene ◽

Repair Gene ◽

Gene Homology

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Cloning and nucleotide sequence of DNA mismatch repair gene PMS1 from Saccharomyces cerevisiae: homology of PMS1 to procaryotic MutL and HexB.

Journal of Bacteriology ◽

10.1128/jb.171.10.5339-5346.1989 ◽

1989 ◽

Vol 171 (10) ◽

pp. 5339-5346 ◽

Cited By ~ 97

Author(s):

W Kramer ◽

B Kramer ◽

M S Williamson ◽

S Fogel

Keyword(s):

Saccharomyces Cerevisiae ◽

Nucleotide Sequence ◽

Mismatch Repair ◽

Dna Mismatch Repair ◽

Mismatch Repair Gene ◽

Repair Gene ◽

Dna Mismatch ◽

Dna Mismatch Repair Gene

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EXO1 and MSH6 Are High-Copy Suppressors of Conditional Mutations in the MSH2 Mismatch Repair Gene of Saccharomyces cerevisiae

Genetics ◽

10.1093/genetics/155.2.589 ◽

2000 ◽

Vol 155 (2) ◽

pp. 589-599 ◽

Cited By ~ 5

Author(s):

Tanya Sokolsky ◽

Eric Alani

Keyword(s):

Saccharomyces Cerevisiae ◽

Mismatch Repair ◽

Central Component ◽

Mismatch Repair Gene ◽

Temperature Sensitive ◽

Repair Gene ◽

Nucleotide Insertion ◽

Catalytic Role ◽

Partial Suppression ◽

Synthetically Lethal

Abstract In Saccharomyces cerevisiae, Msh2p, a central component in mismatch repair, forms a heterodimer with Msh3p to repair small insertion/deletion mismatches and with Msh6p to repair base pair mismatches and single-nucleotide insertion/deletion mismatches. In haploids, a msh2Δ mutation is synthetically lethal with pol3-01, a mutation in the Polδ proofreading exonuclease. Six conditional alleles of msh2 were identified as those that conferred viability in pol3-01 strains at 26° but not at 35°. DNA sequencing revealed that mutations in several of the msh2ts alleles are located in regions with previously unidentified functions. The conditional inviability of two mutants, msh2-L560S pol3-01 and msh2-L910P pol3-01, was suppressed by overexpression of EXO1 and MSH6, respectively. Partial suppression was also observed for the temperature-sensitive mutator phenotype exhibited by msh2-L560S and msh2-L910P strains in the lys2-Bgl reversion assay. High-copy plasmids bearing mutations in the conserved EXO1 nuclease domain were unable to suppress msh2-L560S pol3-01 conditional lethality. These results, in combination with a genetic analysis of msh6Δ pol3-01 and msh3Δ pol3-01 strains, suggest that the activity of the Msh2p-Msh6p heterodimer is important for viability in the presence of the pol3-01 mutation and that Exo1p plays a catalytic role in Msh2p-mediated mismatch repair.

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A defect in mismatch repair in Saccharomyces cerevisiae stimulates ectopic recombination between homeologous genes by an excision repair dependent process.

Genetics ◽

10.1093/genetics/126.3.535 ◽

1990 ◽

Vol 126 (3) ◽

pp. 535-547 ◽

Cited By ~ 2

Author(s):

A M Bailis ◽

R Rothstein

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Repair ◽

Gene Conversion ◽

Mismatch Repair ◽

Excision Repair ◽

Mitotic Recombination ◽

Mismatch Repair Gene ◽

Repair Gene ◽

Ectopic Recombination ◽

Homeologous Genes

Abstract Null mutations in three recombination and DNA repair genes were studied to determine their effects on mitotic recombination between the duplicate AdoMet (S-adenosylmethionine) synthetase genes (SAM1 and SAM2) in Saccharomyces cerevisiae. SAM1 and SAM2, located on chromosomes XII and IV, respectively, encode functionally equivalent although differentially regulated AdoMet synthetases. These similar but not identical (homeologous) genes are 83% homologous at the nucleotide level and this identity is limited solely to the coding regions of the genes. Single frameshift mutations were introduced into the 5' end of SAM1 and the 3' end of SAM2 by restriction site ablation. The sequences surrounding these mutations differ significantly in their degree of homology to the corresponding area of the other gene. Mitotic ectopic recombination between the mutant sam genes occurs at a rate of 8.4 x 10(-9) in a wild-type genetic background. Gene conversion of the marker within the region of greater sequence homology occurs 20-fold more frequently than conversion of the marker within the region of relative sequence diversity. The relative orientation of the two genes prevents the recovery of translocations. Mitotic recombination between the sam genes is completely dependent on the DNA repair and recombination gene RAD52. A mutation in PMS1, a mismatch repair gene, causes a 4.5-fold increase in the rate of ectopic recombination. RAD1, an excision repair gene, is required to observe this increased rate of ectopic conversion. In addition, RAD1 is involved in modulating the pattern of coconversion during recombination between the homeologous sam genes. These results suggest that interactions between mismatch repair, excision repair and recombinational repair functions are involved in determining the ectopic gene conversion frequency between the sam genes.

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