Y-family DNA polymerases respond to DNA damage-independent inhibition of replication fork progression

In Escherichia coli , the Y‐family DNA polymerases Pol IV (DinB) and Pol V (UmuD 2 ′C) enhance cell survival upon DNA damage by bypassing replication‐blocking DNA lesions. We report a unique function for these polymerases when DNA replication fork progression is arrested not by exogenous DNA damage, but with hydroxyurea (HU), thereby inhibiting ribonucleotide reductase, and bringing about damage‐independent DNA replication stalling. Remarkably, the umuC122 ∷Tn 5 allele of umuC , dinB , and certain forms of umuD gene products endow E. coli with the ability to withstand HU treatment (HU R ). The catalytic activities of the UmuC122 and DinB proteins are both required for HU R . Moreover, the lethality brought about by such stalled replication forks in the wild‐type derivatives appears to proceed through the toxin/antitoxin pairs mazEF and relBE . This novel function reveals a role for Y‐family polymerases in enhancing cell survival under conditions of nucleotide starvation, in addition to their established functions in response to DNA damage.