Strand- and replication timing-dependent functions of DNA polymerase η in human DNA replication.

DNA polymerase η preferentially participates in lagging strand replication during unperturbed S phase in human cells, with usage enriched in late-replicating domains.

• Why it matters: Coordinated use of replicative and error-prone polymerases shapes replication flexibility but increases mutagenesis, and Pol η’s broader role beyond UV TLS is unclear.
• What they did: Using polymerase usage sequencing (Pu-seq), Pol η activity was mapped genome-wide during unperturbed replication; strand bias required direct PCNA interaction, and late-domain enrichment depended on PCNA ubiquitylation.
• The result: In cancer genomes, Pol η mutations are enriched in late-replicating regions and correlate with RAD18 expression, linking PCNA ubiquitylation to Pol η–mediated mutagenesis.