Novel PMS1 alleles preferentially affect the repair of primer strand loops during DNA replication

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair

Background:

• DNA mismatch repair (MMR) corrects errors during DNA replication, including insertions and deletions in simple sequence repeats.
• Polymerase slippage can create single-strand loops, which MMR machinery typically repairs.
• MMR is generally more efficient at repairing template strand loops than primer strand loops in yeast and mammalian cells.

Purpose of the Study:

• To investigate the role of Pms1 in the differential repair of primer versus template strand loops during DNA replication.
• To characterize novel yeast pms1 alleles and their specific defects in MMR.

Main Methods:

• Characterization of two novel yeast pms1 alleles (pms1-G882E and pms1-H888R) in Saccharomyces cerevisiae.
• Assessing the repair efficiency of primer and template strand loops in these mutant strains.
• Evaluating the repair of 1-nucleotide loop mispairs during replication and meiotic recombination.

Main Results:

• The identified pms1 alleles specifically impair the repair of primer strand loops while maintaining efficient repair of template strand loops.
• These defects affect primer strand loop repair during both leading and lagging strand replication.
• The pms1 mutants remain proficient in repairing loops generated during meiotic recombination.

Conclusions:

• The inefficiency of primer strand loop repair involves Pms1 and downstream proteins, not solely a mismatch recognition issue.
• These findings highlight a specific role for Pms1 in distinguishing between primer and template strand loops.
• MMR is closely linked to the replication apparatus for effective mutation avoidance.