Mlh2 is an accessory factor for DNA mismatch repair in Saccharomyces cerevisiae

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair

Background:

• The essential mismatch repair (MMR) endonuclease Mlh1-Pms1 in Saccharomyces cerevisiae forms foci promoted by Msh2-Msh6 or Msh2-Msh3 in response to mispaired bases.
• The role of the Mlh1-Mlh2 complex in MMR has been previously unclear.

Purpose of the Study:

• To analyze the Mlh1-Mlh2 complex and elucidate its function in DNA mismatch repair.
• To investigate the relationship between Mlh1-Mlh2 and the essential MMR endonuclease Mlh1-Pms1.

Main Methods:

• Analysis of Mlh1-Mlh2 foci formation, colocalization, and lifetime compared to Mlh1-Pms1.
• Investigating Mlh1-Mlh2 recruitment to mispaired DNA in vitro.
• Assessing mutation rates upon MLH2 deletion in combination with other MMR gene deletions or reduced expression.
• Phylogenetic analysis to determine homology between S. cerevisiae Mlh2 and mammalian PMS1.

Main Results:

• Mlh1-Mlh2 formed foci that colocalized with and had a longer lifetime than Mlh1-Pms1 foci.
• Mlh1-Mlh2 foci formation was dependent on Msh2-Msh6 recognition of mispairs and increased with more mispairs or MMR defects.
• Mlh1-Mlh2 foci formed after phleomycin-induced DNA damage but not double-stranded breaks.
• Deletion of MLH2 synergistically increased mutation rates when combined with MSH6 deletion or PMS1 downregulation.
• Phylogenetic analysis revealed Mlh2 (yeast) and PMS1 (mammalian) are homologs.

Conclusions:

• Mlh1-Mlh2 functions as a non-essential accessory factor in DNA mismatch repair.
• Mlh1-Mlh2 enhances the activity of the essential Mlh1-Pms1 endonuclease.
• The findings suggest a conserved role for Mlh2/PMS1 homologs in MMR pathways across species.