Error-Free DNA Damage Tolerance and Sister Chromatid Proximity during DNA Replication Rely on the Polα/Primase/Ctf4 Complex

Summary

Chromosomal replication is entwined with DNA damage tolerance (DDT) and chromatin structure establishment via elusive mechanisms. Here we examined how specific replication conditions affecting replisome architecture and repriming impact on DDT. We show that Saccharomyces cerevisiae Polα/Primase/Ctf4 mutants, proficient in bulk DNA replication, are defective in recombination-mediated damage-bypass by template switching (TS) and have reduced sister chromatid cohesion. The decrease in error-free DDT is accompanied by increased usage of mutagenic DDT, fork reversal, and higher rates of genome rearrangements mediated by faulty strand annealing. Notably, the DDT defects of Polα/Primase/Ctf4 mutants are not the consequence of increased sister chromatid distance, but are instead caused by altered single-stranded DNA metabolism and abnormal replication fork topology. We propose that error-free TS is driven by timely replicative helicase-coupled re-priming. Defects in this event impact on replication fork architecture and sister chromatid proximity, and represent a frequent source of chromosome lesions upon replication dysfunctions.

Graphical Abstract

Highlights

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  Polα/Primase and cohesin support damage tolerance and sister chromatid proximity

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  Artificial cohesion bypasses cohesin, but not Polα/Primase role in recombination

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  Defects in Polα/Primase cause faulty strand annealing and reversed fork formation

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  Altered ssDNA metabolism underlies Polα/Primase mutants damage tolerance defects

Abstract

Fumasoni et al. explore the interplay between replication, sister chromatid cohesion, and recombination. Recombination and cohesion are facilitated by both cohesin and replication-fork-coupled re-priming. Cohesin does so by keeping the sister chromatids together, whereas replication-fork-coupled re-priming sustains normal fork architecture required for optimal cohesion and recombination-mediated DNA damage tolerance.