Translesion Polymerases Drive Microhomology-Mediated Break-Induced Replication Leading to Complex Chromosomal...

Area of Science:

• Genetics
• Molecular Biology
• Genomic Instability

Background:

• Complex genomic rearrangements (CGRs) are implicated in numerous human diseases.
• Microhomology-mediated break-induced replication (MMBIR) is a proposed mechanism for CGRs, involving template switching at microhomology sites.
• The precise causes and protein mediators of MMBIR remain largely unknown.

Purpose of the Study:

• To elucidate the mechanism and protein players involved in initiating MMBIR.
• To investigate the role of DNA repair pathways in MMBIR.
• To provide mechanistic insights into CGRs relevant to human diseases.

Main Methods:

• Utilized a yeast model system to study DNA repair and recombination.
• Investigated the consequences of Pif1 helicase deficiency on DNA replication and repair.
• Analyzed template switching events and identified the roles of specific translesion synthesis (TLS) polymerases.

Main Results:

• A collapse of homology-driven break-induced replication (BIR) due to defective repair DNA synthesis in Pif1-deficient yeast leads to MMBIR.
• MMBIR involves template switches at 0-6 nucleotide microhomology regions, resulting in chromosomal rearrangements.
• Translesion synthesis (TLS) polymerases, specifically Polζ and Rev1, were identified as key drivers of these microhomology-mediated template switches.

Conclusions:

• Interruption of homologous BIR triggers a switch to MMBIR, catalyzed by TLS polymerases.
• This study provides critical mechanistic insights into the initiation of MMBIR.
• The findings offer a model for understanding CGRs associated with human diseases.