A DNA helicase from Xenopus laevis ovaries.
A DNA helicase was extensively purified from Xenopus laevis ovaries. The most purified fraction was free of DNA topoisomerase, DNA polymerase, and nuclease activities. The enzyme had a Stokes radius of 54 A and a sedimentation coefficient of 6-7.3 S, from which a native molecular weight of 140,000-170,000 was calculated. DNA helicase activity required Mg2+ or Mn2+ and was dependent on hydrolysis of ATP or dATP. Monovalent cations, K+ and Na+, stimulated DNA unwinding with an optimum at 130 mM. DNA-dependent ATPase activity copurified with the X. laevis DNA helicase. Double-stranded and single-stranded DNA were both cofactors for the ATPase activity, but single-stranded DNA was more efficient. The molecular weight, monovalent cation dependence, cofactor requirements, and elution from single-stranded DNA-cellulose suggest that the X. laevis DNA helicase is different from previously described eukaryotic DNA helicases.
Poll
E H
EH
Department of Zoology, Iowa State University, Ames 50011-3223.
Benbow
R M
RM
D000818:Animals; D002413:Cations, Divalent; D002845:Chromatography; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification* / Q000378:metabolism; D017886:Durapatite; D005260:Female; D006882:Hydroxyapatites; D007700:Kinetics; D008970:Molecular Weight; D010053:Ovary / Q000201:enzymology*; D011487:Protein Conformation; D014461:Ultracentrifugation; D014982:Xenopus laevis
D002413:Cations, Divalent; D006882:Hydroxyapatites; D017886:Durapatite; D004264:DNA Topoisomerases, Type I