Multiple HRDC domains modulate the biochemical activity of the Deinococcus radiodurans RecQ helicase

RecQ helicases are key genomic maintenance enzymes that function at the interface between DNA replication, recombination, and repair. The RecQ helicase from the radioresistant bacterium Deinococcus radiodurans encodes a rare triple repeat of a Helicase and RNase D C‐terminal (HRDC) domain at its C‐terminus. RecQ HRDC domains have been implicated in nucleic acid binding and substrate preference in bacteria as well as in higher eukaryotes. We investigated the biochemical functions of the multiple HRDC domains in D. radiodurans RecQ (DrRecQ). We show that the N‐terminal‐most HRDC domain is critical for high affinity DNA binding and is important for efficient DNA unwinding. In contrast, the two C‐terminal HRDC domains are negative regulators of DrRecQ, reducing the enzyme's affinity for DNA and its catalytic activities. Overall, our results indicate that additional HRDC domains act to control DrRecQ function.