A novel DNA helicase with strand-annealing activity from the crenarchaeon Sulfolobus solfataricus

To protect their genetic material cells adopt different mechanisms linked to DNA replication, recombination and repair. Several proteins function at the interface of these DNA transactions. In the present study, we report on the identification of a novel archaeal DNA helicase. BlastP searches of the Sulfolobus solfataricus genome database allowed us to identify an open reading frame (SSO0112, 875 amino acid residues) having sequence similarity with the human RecQ5beta. The corresponding protein, termed Hel112 by us, was produced in Escherichia coli in soluble form, purified to homogeneity and characterized. Gel-filtration chromatography and glycerol-gradient sedimentation analyses revealed that Hel112 forms monomers and dimers in solution. Biochemical characterization of the two oligomeric species revealed that only the monomeric form has an ATP-dependent 3'-5' DNA-helicase activity, whereas, unexpectedly, both the monomeric and dimeric forms possess DNA strand-annealing capability. The Hel112 monomeric form is able to unwind forked and 3'-tailed DNA structures with high efficiency, whereas it is almost inactive on blunt-ended duplexes and bubble-containing molecules. This analysis reveals that S. solfataricus Hel112 shares some enzymatic features with the RecQ-like DNA helicases and suggests potential cellular functions of this protein.