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The yeast gene MSH3 defines a new class of eukaryotic MutS homologues
L New1, K Liu, G F Crouse
1Department of Biology, Emory University, Atlanta, Georgia 30322.
Abstract:
We have identified a gene in Saccharomyces cerevisiae, MSH3, whose predicted protein product shares extensive sequence similarity with bacterial proteins involved in DNA mismatch repair as well as with the predicted protein product of the Rep-3 gene of mouse. MSH3 was obtained by performing a polymerase chain reaction on yeast genomic DNA using degenerate oligonucleotide primers designed to anneal with the most conserved regions of a gene that would be homologous to Rep-3 and Salmonella typhimurium mutS. MSH3 seems to play some role in DNA mismatch repair, inasmuch as its inactivation results in an increase in reversion rates of two different mutations and also causes an increase in postmeiotic segregation. However, the effect of MSH3 disruption on reversion rates and postmeiotic segregation appears to be much less than that of previously characterized yeast DNA mismatch repair genes. Alignment of the MSH3 sequence with all of the known MutS homologues suggests that its primary function may be different from the role of MutS in repair of replication errors. MSH3 appears to be more closely related to the mouse Rep-3 gene and other similar eukaryotic mutS homologues than to the yeast gene MSH2 and other mutS homologues that are involved in replication repair. We suggest that the primary function of MSH3 may be more closely related to one of the other known functions of mutS, such as its role in preventing recombination between non-identical sequences.
Insights
Researchers identified the Saccharomyces cerevisiae MSH3 gene, involved in DNA mismatch repair. While MSH3 plays a role, its function appears distinct from other known yeast mismatch repair genes.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA mismatch repair (MMR) is crucial for genomic stability.
- Homologs of bacterial MutS proteins are key components of MMR systems in eukaryotes.
- Previous studies identified yeast MMR genes like MSH2.
Purpose of the Study:
- To identify and characterize novel genes involved in DNA mismatch repair in Saccharomyces cerevisiae.
- To investigate the function of the newly identified MSH3 gene in DNA repair and genetic stability.
Main Methods:
- Polymerase chain reaction (PCR) using degenerate primers.
- Screening of yeast genomic DNA for homology to bacterial MutS and mouse Rep-3.
- Analysis of mutation reversion rates and postmeiotic segregation in MSH3-disrupted yeast strains.
Main Results:
- Identified the Saccharomyces cerevisiae MSH3 gene, homologous to bacterial MutS and mouse Rep-3.
- MSH3 inactivation led to increased reversion rates and postmeiotic segregation, but to a lesser extent than other MMR genes.
- Sequence alignment suggests MSH3's primary function may differ from replication error repair.
Conclusions:
- MSH3 is a novel gene in yeast with a role in DNA mismatch repair.
- Its function may be more closely related to preventing recombination between non-identical sequences than replication error repair.
- MSH3 represents a distinct branch of eukaryotic MutS homologs.