Alleles of the yeast Pms1 mismatch-repair gene that differentially affect recombination- and replication-related...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Eukaryotic genome stability relies on mismatch-repair (MMR) systems, which correct DNA replication errors and prevent recombination between non-identical sequences.
• MMR involves MutS-homologous Msh proteins for mismatch recognition and MutL homologs, like the yeast Mlh1p-Pms1p heterodimer, for downstream processing.
• The specific roles of ATPase activity in MMR's distinct functions (spellchecking and anti-recombination) remain to be fully elucidated.

Purpose of the Study:

• To investigate whether the processing steps in the MMR spellchecker and antirecombination pathways differ.
• To determine the specific roles of Pms1p and Mlh1p ATPase activities in MMR-related processes, including replication error repair and recombination inhibition.
• To identify separation-of-function alleles of the yeast PMS1 gene.

Main Methods:

• Mutagenesis of the yeast PMS1 gene and screening for mitotic separation-of-function alleles.
• Analysis of mutations compromising the ATPase activity of Pms1p and Mlh1p.
• Assessment of spellchecker and antirecombination activities in mitotic cells and repair of meiotic recombination intermediates.

Main Results:

• Two PMS1 alleles were identified that specifically affected the antirecombination function, with one altering the conserved ATPase domain.
• Pms1p ATPase activity showed a differential requirement between replication and recombination processes.
• Mlh1p ATPase activity was essential for all investigated MMR-related functions.

Conclusions:

• The ATPase activity of Pms1p plays distinct roles in the spellchecker and antirecombination functions of MMR.
• Mlh1p's ATPase activity is universally required for MMR, highlighting its central role in maintaining genome integrity.
• These findings provide insights into the mechanistic basis of MMR pathway specificity and regulation.