Requirement of the Yeast MSH3 and MSH6 Genes for MSH2-dependent Genomic Stability

Robert E Johnson,Gopala K Kovvali,Louise Prakash,Satya Prakash

doi:10.1074/jbc.271.13.7285

Robert E Johnson, Gopala K Kovvali + Show 2 more

Open Access

https://doi.org/10.1074/jbc.271.13.7285

Copy DOI

Abstract

Defects in DNA mismatch repair result in instability of simple repetitive DNA sequences and elevated levels of spontaneous mutability. The human G/T mismatch binding protein, GTBP/p160, has been suggested to have a role in the repair of base-base and single nucleotide insertion-deletion mismatches. Here we examine the role of the yeast GTBP homolog, MSH6, in mismatch repair. We show that both MSH6 and MSH3 genes are essential for normal genomic stability. Interestingly, although mutations in either MSH3 or MSH6 do not cause the extreme microsatellite instability and spontaneous mutability observed in the msh2 mutant, yeast cells harboring null mutations in both the MSH3 and MSH6 genes exhibit microsatellite instability and mutability similar to that in the msh2 mutant. Results from epistasis analyses indicate that MSH2 functions in mismatch repair in conjunction with MSH3 or MSH6 and that MSH3 and MSH6 constitute alternate pathways of MSH2-dependent mismatch repair.

Highlights

Predisposition is not entirely clear at present, because two of the colorectal cancer cell lines, DLD-1 and HCT-15 that are mutated in GTBP, harbor mutations in the 3Ј–5Ј-exonuclease “proofreading” domain of Deletion mutations were confirmed by Southern (DNA) polymerase ␦ [16]
The observed phenotypes in these cell lines could arise from the mutations in GTBP or those in pol␦, or they could be due to the combined effects of the GTBP and pol␦ mutations
To clarify the roles of the MSH2, MSH3, and MSH6 genes in mismatch repair and to identify the possible functional interaction among them, we have examined the effects of null mutations in these genes on microsatellite instability and spontaneous mutability and have carried out epistasis analyses

Summary

Introduction

Predisposition is not entirely clear at present, because two of the colorectal cancer cell lines, DLD-1 and HCT-15 that are mutated in GTBP, harbor mutations in the 3Ј–5Ј-exonuclease “proofreading” domain of DNA polymerase ␦ [16]. In Saccharomyces cerevisiae, mutations in the mismatch repair genes MSH2, PMS1, or MLH1 result in marked increases in spontaneous mutation rates and microsatellite instability [17,18,19,20]. Mutations in MSH3, another MSH2 homolog, cause a moderate increase in microsatellite instability [24] and have little effect on spontaneous forward mutation rates [25]. To clarify the roles of the MSH2, MSH3, and MSH6 genes in mismatch repair and to identify the possible functional interaction among them, we have examined the effects of null mutations in these genes on microsatellite instability and spontaneous mutability and have carried out epistasis analyses. Our studies indicate that for its function in mismatch repair, MSH2 requires the MSH3 or the MSH6 gene and that MSH3 and MSH6 constitute alternate MSH2-dependent mismatch repair pathways

Methods

Results

Conclusion