Migrating bubble synthesis promotes mutagenesis through lesions in its template

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair

Background:

• Break-induced replication (BIR) is a mutagenic DNA repair pathway.
• Long single-stranded (ss) nascent DNA is a known source of BIR mutagenesis.
• Understanding all ssDNA sources in BIR is crucial for explaining its mutagenicity.

Purpose of the Study:

• To identify novel sources of mutagenic single-stranded DNA (ssDNA) during break-induced replication (BIR).
• To investigate the role of the D-loop bottom template strand (D-BTS) in BIR mutagenesis.
• To explore additional mechanisms of genetic instability during BIR.

Main Methods:

• Investigated DNA lesions induced by APOBEC3A (A3A) on ssDNA during BIR.
• Analyzed replication slippage between microhomologies stimulated by inverted DNA repeats.
• Characterized the D-loop bottom template strand (D-BTS) as a source of mutagenic ssDNA.

Main Results:

• Identified the D-loop bottom template strand (D-BTS) as a novel source of mutagenic ssDNA during BIR.
• Demonstrated D-BTS susceptibility to APOBEC3A (A3A)-induced DNA lesions, causing BIR-associated mutations.
• Showed that BIR-associated ssDNA promotes replication slippage, leading to genetic instability.

Conclusions:

• The D-loop bottom template strand (D-BTS) is a significant source of mutagenesis during break-induced replication (BIR).
• BIR involves multiple ssDNA sources, including nascent DNA and D-BTS, contributing to genetic instability.
• This newly identified mutagenic pathway may be relevant to other D-loop-driven homologous recombination processes.