Physical interactions between MCM and Rad51 facilitate replication fork lesion bypass and ssDNA gap filling by non-recombinogenic functions

The minichromosome maintenance (MCM) helicase physically interacts with the recombination proteins Rad51 and Rad52 from yeast to human cells. We show, in Saccharomyces cerevisiae, that these interactions occur within a nuclease-insoluble scaffold enriched in replication/repair factors. Rad51 accumulates in a MCM- and DNA-binding-independent manner and interacts with MCMhelicases located outside of the replication origins and forks. MCM, Rad51, and Rad52 accumulate in this scaffold in G1 and are released during the S phase. In the presence of replication-blocking lesions, Cdc7 prevents their release from the scaffold, thus maintaining the interactions. We identify a rad51 mutant that is impaired in its ability to bind to MCM but not to the scaffold. This mutant is proficient in recombination but partially defective in single-stranded DNA (ssDNA) gap filling and replication fork progression through damaged DNA. Therefore, cells accumulate MCM/Rad51/Rad52 complexes at specific nuclear scaffolds in G1 to assist stressed forks through non-recombinogenic functions.

Automated summary

The study demonstrates that the minichromosome maintenance (MCM) helicase interacts with the recombination proteins Rad51 and Rad52 from yeast to human cells within a nuclease-insoluble scaffold enriched in replication/repair factors. Rad51, Rad52, and MCM accumulate in this scaffold in G1 and are released during the S phase, with Cdc7 preventing their release in the presence of replication-blocking lesions. Additionally, a rad51 mutant is identified which is impaired in binding to MCM but proficient in recombination, partially defective in single-stranded DNA gap filling and replication fork progression through damaged DNA. This highlights a mechanism by which cells accumulate MCM/Rad51/Rad52 complexes at specific nuclear scaffolds in G1 to aid in stressed fork progression through non-recombinogenic functions.