The fission yeast Pfh1 DNA helicase promotes fork progression through multiple types of replication obstacles (236.1)

Abstract

The fission yeast Pfh1, an essential 5’ to 3’ helicase, is a member of the highly conserved Pif1 family of DNA helicases. Mutation of human PIF1 (hPIF1) within the 21 amino acid Pif1 signature motif is associated with elevated cancer risk, suggesting that hPIF1 is a tumor suppressor gene. Like budding yeast Pif1 family helicases, S. pombe Pfh1 has a key role in DNA replication. By both mass spectrometry and in vivo experiments, Pfh1 is a replisome component. By chromatin immune‐precipitation plus deep sequencing, cells depleted of Pfh1 have increased fork pausing and DNA damage near many hard to replicate sites, as indicated by high DNA polymerase occupancy and phosphorylated histone H2A, respectively. These sites include highly transcribed genes, telomeres, and sequences able to form G‐quadruplex (G4) structures in vivo. Pfh1 suppresses G4‐induced gross chromosomal rearrangements in Pif1 helicase deficient budding yeast while Pfh1‐L430P, which has the mutation associated with human cancer, does not. These data suggest that in the absence of Pfh1, replication pausing and DNA damage results in genome instability of the sort associated with human tumors.