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Redundancy of Saccharomyces cerevisiae MSH3 and MSH6 in MSH2-dependent mismatch repair
G T Marsischky1, N Filosi, M F Kane
1Charles A. Dana Division of Human Cancer Genetics, Dana-Farber Cancer Institute, Boston, Massachusetts 02115 USA.
Abstract:
Saccharomyces cerevisiae encodes six genes, MSH1-6, which encode proteins related to the bacterial MutS protein. In this study the role of MSH2, MSH3, and MSH6 in mismatch repair has been examined by measuring the rate of accumulating mutations and mutation spectrum in strains containing different combinations of msh2, msh3, and msh6 mutations and by studying the physical interaction between the MSH2 protein and the MSH3 and MSH6 proteins. The results indicate that S. cerevisiae has two pathways of MSH2-dependent mismatch repair: one that recognized single-base mispairs and requires MSH2 and MSH6, and a second that recognizes insertion/deletion mispairs and requires a combination of either MSH2 and MSH6 or MSH2 and MSH3. The redundancy of MSH3 and MSH6 explains the greater prevalence of hmsh2 mutations in HNPCC families and suggests how the role of hmsh3 and hmsh6 mutations in cancer susceptibility could be analyzed.
Insights
This study reveals two DNA mismatch repair pathways in Saccharomyces cerevisiae, involving MSH2, MSH3, and MSH6 proteins. These pathways address different types of DNA errors, impacting mutation accumulation and cancer susceptibility research.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Saccharomyces cerevisiae possesses six MSH genes (MSH1-6) encoding proteins homologous to bacterial MutS.
- DNA mismatch repair (MMR) is crucial for maintaining genomic stability.
- Understanding MMR pathways is vital for cancer research, particularly hereditary nonpolyposis colorectal cancer (HNPCC).
Purpose of the Study:
- To investigate the roles of MSH2, MSH3, and MSH6 in Saccharomyces cerevisiae mismatch repair.
- To elucidate the distinct pathways of DNA mismatch repair.
- To explore the implications of these pathways for understanding mutation accumulation and cancer susceptibility.
Main Methods:
- Mutation accumulation assays in yeast strains with various msh2, msh3, and msh6 mutation combinations.
- Analysis of mutation spectra to identify repair pathway specificities.
- Co-immunoprecipitation studies to examine physical interactions between MSH2, MSH3, and MSH6 proteins.
Main Results:
- Identified two distinct MSH2-dependent mismatch repair pathways in S. cerevisiae.
- Pathway 1 recognizes single-base mispairs and requires MSH2 and MSH6.
- Pathway 2 recognizes insertion/deletion mispairs and requires either MSH2/MSH6 or MSH2/MSH3.
Conclusions:
- The MSH3 and MSH6 proteins exhibit functional redundancy in mismatch repair.
- This redundancy helps explain the higher frequency of MSH2 mutations in HNPCC.
- Further analysis of MSH3 and MSH6 roles can advance understanding of cancer susceptibility.