Replisome bypass of a protein-based R-loop block by Pif1
Grant D. Schauer, Lisanne M. Spenkelink, Jacob S. Lewis, Olga Yurieva, S.H. Mueller, Antoine M. van Oijen, Mike O’Donnell
Abstract
Significance The replisome machine that duplicates the DNA genome encounters a variety of blocks to replication, such as DNA bound proteins, R-loops, and DNA lesions. Studies in bacterial systems demonstrate that replisome advance through blocks is facilitated by an accessory monomeric helicase that acts on the opposite strand from the replicative hexameric helicase. This report examines this issue in a eukaryotic system, using Pif1, a monomeric helicase that acts on the opposite strand from the replicative CMG helicase. The report shows that an inactive “dead” Cas9 (dCas9) protein R-loop block arrests the replisome, but Pif1 enables replisome bypass of the dCas9 R-loop block. Hence, use of monomeric helicases may have evolved to aid replisome bypass of protein-DNA and protein-bound R-loop blocks.