DNA-dependent adenosinetriphosphatase B from mouse FM3A cells has DNA helicase activity.

Abstract

We have detected at least four forms of DNA-dependent ATPase in mouse FM3A cell extracts [Tawaragi, Y., Enomoto, T., Watanabe, Y., Hanaoka, F., & Yamada, M. (1984) Biochemistry 23, 529-533]. The purified fraction of one of the four forms, ATPase B, has been shown to have DNA helicase activity by using a DNA substrate which permits the detection of limited unwinding of the helix. The DNA substrate consists of single-stranded circular fd DNA and the hexadecamer complementary to the fd DNA, which bears an oligo(dT) tail at the 3' terminus. The helicase activity and DNA-dependent ATPase activity cosedimented at 5.5 S on glycerol gradient centrifugation. The helicase required a divalent cation for activity (Mg2+ congruent to Mn2+ greater than Ca2+). The optimal concentrations of these divalent cations were 5 mM. The requirement of divalent cations of the DNA helicase activity was very similar to that for the DNA-dependent ATPase activity of ATPase B. The helicase activity was absolutely dependent on the presence of a nucleoside triphosphate. ATP was the most effective cofactor among the ribo- and deoxyribonucleoside triphosphates tested, and considerable levels of helicase activity were observed with other ribo- and deoxyribonucleoside triphosphates. The efficiency of a nucleoside triphosphate to serve as cofactor for the helicase activity correlated with the capacity of the nucleotide to serve as substrate for the DNA-dependent ATPase activity. The nonhydrolyzable ATP analogues such as adenosine 5'-O-(3-thiotriphosphate) were not effective for the helicase activity.(ABSTRACT TRUNCATED AT 250 WORDS)