Physical interaction between archaeal DNA repair helicase Hel308 and Replication Protein A (RPA)

Hel308 is a super-family 2 helicase in archaea with homologues in higher eukaryotes (HelQ and PolQ) that contribute to repair of DNA strand crosslinks (ICLs). However, the contribution of Hel308 to repair processes in archaea is far from clear, including how it co-operates with other proteins of DNA replication, repair and recombination. In this study we identified a physical interaction of Hel308 with RPA. Hel308 did not interact with SSB, and interaction with RPA required a conserved amino acid motif at the Hel308 C-terminus. We propose that in archaea RPA acts as a platform for loading of Hel308 onto aberrant single-stranded DNA (ssDNA) that arises at blocked replication forks. In line with data from a human Hel308 homologue, the helicase activity of archaeal Hel308 was only modestly stimulated (1.5-2 fold) by RPA under some conditions, and much less so than for other known interactions between helicases and single strand DNA (ssDNA) binding proteins. This supports a model for RPA localising Hel308 to DNA damage sites in archaea, rather than it directly stimulating the mechanism of helicase unwinding.