Characterization of a helicase, DHEL III, from Drosophila melanogaster embryonic nuclei.

Nuclear extracts prepared from Drosophila preblastoderm embryos contain a nucleoside 5'-triphosphate-dependent helicase that unwinds circular or linear partial duplex DNA substrates and moves along the DNA in 3' to 5' direction. The helicase reaction is supported with both nucleoside and deoxynucleoside 5'-triphosphates and requires divalent cations. Optimum activity in vitro is achieved with dATP or ATP and with MgCl2. In glycerol density gradients, embryonic enzyme migrates as a single peak of around 90kDa and it is the most prominent DNA-unwinding activity detectable in nuclear extracts prepared from embryos 0-2 hours after egg laying. In embryos collected 2-4 hours after egg laying this DNA unwinding activity increases and then gradually decreases in embryos collected 4-8 and 8-16 hours after egg laying.