Evidence That the DNA Mismatch Repair System Removes 1-Nucleotide Okazaki Fragment Flaps

• Published in: The Journal of biological chemistry 2015-10, Vol.290 (40), p.24051-24065
• Main Authors: Kadyrova, Lyudmila Y., Dahal, Basanta K., Kadyrov, Farid A.
• Format: Article
• Language: English
• Subjects: cancer; DNA - chemistry; DNA - genetics; DNA and Chromosomes; DNA endonuclease; DNA Mismatch Repair; DNA Mutational Analysis; DNA Repair Enzymes - metabolism; DNA Replication; DNA, Circular - chemistry; Flap Endonucleases - genetics; Fungal Proteins - metabolism; Gene Deletion; Genome; genomic instability; Humans; Mutation; mutL homolog 1 (MLH1); MutL Proteins; MutS DNA Mismatch-Binding Protein - metabolism; Okazaki fragment maturation; Ploidies; Proliferating Cell Nuclear Antigen - metabolism; Protein Structure, Tertiary; Replication Protein C - metabolism; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - metabolism; Substrate Specificity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.660357

The DNA mismatch repair (MMR) system plays a major role in promoting genome stability and suppressing carcinogenesis. In this work, we investigated whether the MMR system is involved in Okazaki fragment maturation. We found that in the yeast Saccharomyces cerevisiae, the MMR system and the flap endonuclease Rad27 act in overlapping pathways that protect the nuclear genome from 1-bp insertions. In addition, we determined that purified yeast and human MutSα proteins recognize 1-nucleotide DNA and RNA flaps. In reconstituted human systems, MutSα, proliferating cell nuclear antigen, and replication factor C activate MutLα endonuclease to remove the flaps. ATPase and endonuclease mutants of MutLα are defective in the flap removal. These results suggest that the MMR system contributes to the removal of 1-nucleotide Okazaki fragment flaps. Background: The DNA mismatch repair (MMR) system protects humans from cancer. Results: Combining an MMR system defect (msh2Δ) with rad27Δ causes a strong synergistic increase in the rate of 1-bp insertions, and a reconstituted MMR system removes 1-nt flaps. Conclusion: The MMR system removes 1-nt Okazaki fragment flaps. Significance: A new function of the MMR system was identified.