Replication fork binding triggers structural changes in the PriA helicase that govern DNA replication restart in E. coli

Abstract

Bacterial replisomes often dissociate from replication forks before chromosomal replication is complete. To avoid the lethal consequences of such situations, bacteria have evolved replication restart pathways that reload replisomes onto prematurely terminated replication forks. To understand how the primary replication restart pathway in E. coli (PriA-PriB) selectively acts on replication forks, we determined the cryogenic-electron microscopy structure of a PriA/PriB/replication fork complex. Replication fork specificity arises from extensive PriA interactions with each arm of the branched DNA. These interactions reshape the PriA protein to create a pore encircling single-stranded lagging-strand DNA while also exposing a surface of PriA onto which PriB docks. Together with supporting biochemical and genetic studies, the structure reveals a switch-like mechanism for replication restart initiation in which restructuring of PriA directly couples replication fork recognition to PriA/PriB complex formation to ensure robust and high-fidelity replication re-initiation.

Hachiman is a genome integrity sensor

“…In the midsection of the duplex, a 'pin' reminiscent of the strand unwinding wedge in the PriA primosomal helicase lies in the center of the duplex and pries the strands apart by pi stacking and physical occlusion (Fig. S5J) 36,37 . Observation of a 3' end in the entry site of the helicase is consistent with the 3' OH preference determined from in vitro assays (Fig.…”