Deinococcus radiodurans PriA is a Pseudohelicase.

Matthew E Lopper,Christopher Morrow,Jacob Boone,Sergey Korolev

doi:10.1371/journal.pone.0133419

Abstract

Reactivation of repaired DNA replication forks in bacteria is catalyzed by PriA helicase. This broadly-conserved bacterial enzyme can remodel the structure of DNA at a repaired DNA replication fork by unwinding small portions of duplex DNA to prepare the fork for replisome reloading. While PriA’s helicase activity is not strictly required for cell viability in E. coli, the sequence motifs that confer helicase activity upon PriA are well-conserved among sequenced bacterial priA genes, suggesting that PriA’s duplex DNA unwinding activity confers a selective advantage upon cells. However, these helicase sequence motifs are not well-conserved among priA genes from the Deinococcus-Thermus phylum. Here, we show that PriA from a highly radiation-resistant member of that phylum, Deinococcus radiodurans, lacks the ability to hydrolyze ATP and unwind duplex DNA, thus qualifying D. radiodurans PriA as a pseudohelicase. Despite the lack of helicase activity, D. radiodurans PriA has retained the DNA binding activity expected of a typical PriA helicase, and we present evidence for a physical interaction between D. radiodurans PriA and its cognate replicative helicase, DnaB. This suggests that PriA has retained a role in replisome reloading onto repaired DNA replication forks in D. radiodurans despite its lack of helicase activity.

Highlights

PriA helicase catalyzes reloading of the DNA replication machinery at repaired DNA replication forks in bacteria, giving bacterial cells the ability to restart DNA replication following disruptive encounters of the replisome with DNA damage [1]
Some bacteria have evolved multiple DNA replication restart pathways that are catalyzed by different sets of primosome proteins and that operate on different types of DNA structures [2, 3]
In E. coli, a PriA-dependent DNA replication restart pathway catalyzes replisome reloading onto forked DNA structures that lack a gap at the three-way fork junction, while a PriC-dependent DNA replication restart pathway facilitates replisome reloading onto DNA structures that contain a leading strand gap at the fork junction [3]

Summary

Introduction

PriA helicase catalyzes reloading of the DNA replication machinery (the replisome) at repaired DNA replication forks in bacteria, giving bacterial cells the ability to restart DNA replication following disruptive encounters of the replisome with DNA damage [1]. We cloned the priA gene from Deinococcus radiodurans R1, expressed and purified recombinant D. radiodurans PriA protein, and tested it for its ability to catalyze ATP hydrolysis and duplex DNA unwinding.

Results

Conclusion