Instability throughout the Saccharomyces cerevisiae genome resulting from Pms1 endonuclease deficiency

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• The endonuclease activity of Pms1 is essential for DNA mismatch repair (MMR) by nicking the newly replicated DNA strand.
• Inactivation of Pms2, the human homolog of Pms1, is linked to increased risks of colorectal and uterine cancers.

Purpose of the Study:

• To investigate the impact of Pms1 endonuclease activity loss on mutation rates and spectra in Saccharomyces cerevisiae.
• To compare the role of Pms1 endonuclease activity in MMR with initial mismatch recognition by Msh2 heterodimers.

Main Methods:

• Whole genome sequencing was employed to analyze mutation patterns in yeast strains with a non-functional Pms1 endonuclease (pms1-DE variant).
• Mutation rates were assessed in strains with pms1-DE, alone and in combination with mutator variants of leading and lagging strand replicases.
• Mutation characteristics were compared to strains lacking MSH2, which impairs initial mismatch recognition.

Main Results:

• Loss of Pms1 endonuclease activity (pms1-DE) caused significant increases in mutation rates across all single-base substitutions and various indel mutations.
• Combining pms1-DE with mutator replicases further elevated mutation rates.
• Mutation profiles in pms1-DE strains were statistically indistinguishable from those lacking MSH2, indicating equivalent importance in MMR.

Conclusions:

• Pms1 endonuclease activity is critical for MMR and genomic stability, comparable in importance to Msh2-mediated mismatch recognition.
• The findings underscore the significance of strand discrimination by Pms1 in preventing mutations genome-wide.
• This research provides insights into the mechanisms underlying cancer development due to MMR deficiencies.