DNA Rereplication Is Susceptible to Nucleotide-Level Mutagenesis

Area of Science:

• Genetics
• Molecular Biology
• Cancer Research

Background:

• Genome instability is a hallmark of cancer, with DNA rereplication identified as a potential contributor.
• Previous studies in *Saccharomyces cerevisiae* demonstrated rereplication's potent induction of gross chromosomal alterations due to fork breakage.

Purpose of the Study:

• To investigate the capacity of DNA rereplication to induce nucleotide-level mutations.
• To elucidate the mechanisms underlying rereplication-induced mutagenesis.

Main Methods:

• Utilized the *lys2InsE* frameshift reporter and the *CAN1* mutagenesis reporter in *Saccharomyces cerevisiae*.
• Assessed mutation rates under conditions of normal replication, rereplication, and with inactivated DNA polymerase ε proofreading.
• Examined the role of mismatch repair in rereplication-induced mutagenesis.

Main Results:

• Rereplication elevated frameshift mutation rates up to 30-fold, primarily due to fork passage, not breakage.
• Rereplication induced comparable frameshift and base-substitution mutations in *CAN1* when proofreading was impaired.
• Rereplication-induced mutagenesis was abolished in the absence of mismatch repair.

Conclusions:

• DNA rereplication facilitates nucleotide-level mutagenesis in addition to gross chromosomal alterations.
• Mismatch repair appears attenuated during rereplication, contributing to increased mutation rates.
• These findings expand the understanding of rereplication's role in genome instability and cancer development.