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Abstract: recQ is a highly conserved helicase necessary for maintaining genome stability in all organisms. Genome comparison showed that a homologue of recQ in Deinococcus radiodurans designated as DR1289 is a member of recQ family with unusual domain arrangement: a helicase domain, an recQ C-terminal domain, and surprisingly three HRDC domain repeats, whose function, however, remains obscure currently. Using an insertion deletion, we discovered that the DRrecQ mutation causes an increase in gamma radiation, hydroxyurea and mitomycine C and UV sensitivity. Using the shuttle plasmid pRADK, we complemented various domains of the D. radiodurans recQ (DRrecQ) to the mutant in vivo. Results suggested that both the helicase and helicase-and-RNase-D-C-terminal (HRDC) domains are essential for complementing several phenotypes. The complementation and biochemical function of DRrecQ variants with different domains truncated in vitro suggested that both the helicase and three HRDC domains are necessary for recQ functions in D. radiodurans, while three HRDC domains have a synergistic effect on the whole function. Our finding leads to the hypothesis that the RecF recombination pathway is likely a primary path of double strand break repair in this well-known radioresistant organism.

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