DNA-dependent ATPase activity associated with vaccinia virus early transcription factor

Abstract

Vaccinia virus early transcription factor (VETF) is required for efficient expression of the early class of viral genes in vitro. The factor copurified with an ATPase activity that was stimulated by DNA. In this report we show that the ATPase remains associated with the factor upon glycerol gradient sedimentation. Under these conditions VETF sedimented at a rate of 7.6 S suggesting that it may be a heterodimer of the Mr 82,000 and 77,000 polypeptides. Of the common nucleoside triphosphates, only ATP and dATP were hydrolyzed by the VETF-associated ATPase. The ATP analog gamma-thio ATP was not a substrate. The VETF-associated ATPase activity was stimulated up to 30-fold by the presence of polynucleotides. DNA was a much more effective cofactor for the ATPase than was RNA, and duplex polydeoxyribonucleotides were preferred. The enzymatic and physical properties of the VETF-associated ATPase distinguished it from all three vaccinia ATPase activities previously described, nucleoside triphosphate phosphohydrolases I and II, and capping enzyme. Except for the preference for double-stranded DNA, the substrate and cofactor requirements of the VETF-associated ATPase most closely resembled those of nucleoside triphosphate phosphohydrolase I. However, VETF-ATPase was not inhibited by polyclonal antibody to the latter enzyme. The association of an ATPase with an early gene transcription factor may explain the previously described requirement for ATP hydrolysis in transcription.