Defects in DNA lesion bypass lead to spontaneous chromosomal rearrangements and increased cell death

Area of Science:

• Molecular Biology
• Genetics
• DNA Repair

Background:

• Rev3 polymerase and Mph1 helicase are key players in DNA lesion bypass pathways.
• Understanding their roles is crucial for maintaining genome stability and preventing mutations.

Purpose of the Study:

• Investigate the roles of Rev3 and Mph1 in genome stability.
• Examine their genetic interactions with recombination factors, helicases, and checkpoint proteins.
• Determine their contribution to viability and methyl methanesulfonate (MMS) sensitivity.

Main Methods:

• Genetic analysis of deletion mutants (rev3Δ, mph1Δ) and their combinations.
• Assessment of spontaneous gross chromosomal rearrangements (GCRs).
• Evaluation of sensitivity to methyl methanesulfonate (MMS).
• Analysis of interactions with homologous recombination (HR) genes (Rad51, Rad52, Rad59), other helicases (Chl1, Rrm3, Sgs1), and checkpoint proteins (Mec3).

Main Results:

• Cells lacking both Rev3 and Mph1 show a synergistic increase in GCRs, dependent on Srs2.
• Mph1 acts epistatically to HR genes, but Rad51 and Rad52 are essential for rev3Δ mutant growth and survival during MMS exposure.
• Mph1 functions in a Rad51-dependent, Rad59-independent HR subpathway for lesion bypass.
• mph1Δ exhibits synergistic DNA damage sensitivity with chl1Δ or rrm3Δ mutations, but is hypostatic to sgs1Δ.
• mph1Δ srs2Δ slow growth and G2/M arrest are suppressed by disrupting the Mec3-dependent DNA damage checkpoint.

Conclusions:

• The suppression of point mutations by REV3 deletion may lead to chromosomal rearrangements.
• Mph1 plays a critical role in a homologous recombination pathway for DNA lesion bypass.
• A model integrating translesion synthesis and HR explains replication fork rescue, with Mph1 unwinding D-loops and interacting with Rev3 and Srs2 pathways to suppress genome instability.