Helicase and DNA-strand annealing activities of Hrq1 cooperate to resolve bulge loop structures generated during DNA replication and recombination

초록

Hrq1 helicase is a novel member of the RecQ family. Among the five human RecQ helicases, Hrq1 is most homologous to RECQL4 and is conserved in fungal genomes. Recent genetic and biochemical studies have shown that it is a functional gene, involved in the maintenance of genome stability. We have reported that Hrq1 is an active helicase stimulated by the presence of a long 3’-single stranded DNA. Here we show Hrq1 displays structure-specific DNA helicase activity that preferentially unwinds bulge-loop structures. It requires a top strand complementary to the bottom strand to displace the bulge-loop DNA, demonstrating that the DNA-strand annealing activity assists helicase activity. We also found that Hrq1 preferentially binds and unwinds DNA substrates containing simple sequence repeats. Our results suggest that Hrq1 may function in the maintenance of stability of repetitive DNA domains by resolving bulge-loop structures resulting from slippage of template DNA during DNA synthesis.