ISOLATION AND CHARACTERIZATION OF DHEL II, A DNA HELICASE FROM DROSOPHILA-MELANOGASTER EMBRYOS STIMULATED BY ESCHERICHIA COLI-TYPE SINGLE-STRANDED-DNA-BINDING PROTEINS

We have purified a DNA helicase from Drosophila embryos by following u nwinding activity during the purification of the cellular single-stran ded DNA-binding protein dRP-A. This DNA helicase unwinds DNA 5' to 3', has a salt-tolerant activity, and has a preference for purine triphos phates as cofactors for the unwinding reaction. The purified enzyme co nsists of a single polypeptide of 120 kDa, which cosediments with the helicase activity. Sedimentation analysis suggests that this polypepti de exists as a monomer under high and low salt conditions. Dhel II is able to unwind long stretches of DNA, but with decreased efficiency. A ddition of Escherichia coli-like single-stranded DNA-binding proteins stimulates the unwinding activity at least 10-fold on substrates great er than 200 nucleotides. In particular, the mitochondrial single-stran ded DNA-binding protein isolated from Drosophila embryos is able to st imulate unwinding by dhel II. These properties show that the helicase described is different from another Drosophila helicase dhel I; it has thus has been classified as dhel II.