Reverse gyrase recruitment to DNA after UV light irradiation in Sulfolobus solfataricus

Induction of DNA damage triggers a complex biological response concerning not only repair systems, but also virtually every cell function. DNA topoisomerases regulate the level of DNA supercoiling in all DNA transactions. Reverse gyrase is a peculiar DNA topoisomerase, specific of hyperthermophilic microorganisms, containing a helicase and a topoisomerase IA domain, which has the unique ability of introducing positive supercoiling into DNA molecules. We show here that reverse gyrase of the archaeon Sulfolobus solfataricus is mobilized to DNA in vivo after UV irradiation. The enzyme, either purified or in cell extracts, forms stable covalent complexes with UV-damaged DNA in vitro. We also show that the reverse gyrase translocation to DNA in vivo and stabilization of covalent complexes in vitro are specific effects of UV irradiation and do not occur with the intercalating agent actinomycin D. Our results suggest that reverse gyrase might participate, directly or indirectly, in the cell response to UV-induced DNA damage. This is the first direct evidence of recruitment of a topoisomerase IA enzyme to DNA after induction of DNA damage. The interaction between helicase and topoisomerase activities has been previously proposed to facilitate aspects of DNA replication or recombination in both Bacteria and eukaryotes. Our results suggest a general role of the association of such activities in maintaining genome integrity and a mutual effect of DNA topology and repair.