Deinococcus radiodurans PriA is a Pseudohelicase

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.