JBC, Vol. 252, Issue 4, 1375-1380, Feb, 1977
Characterization of the nucleoside triphosphate phosphohydrolase (ATPase) activity of RNA synthesi termination factor p. I. Enzymatic properties and effects of inhibitors
C. Lowery and J. P. Richardson
The purification of p protein to homogeneity from Escherichia coli has
shown that its RNA-dependent ATPase activity is physically inseparable from
its termination activity. The biochemical properties of pATPase have been
studied using poly(C) as the activating RNA. This reaction is stimulated by
Mg2+ ions and Mn2+ ions and is prevented by excess EDTA; it is not
stimulated by Ca2+ ions. The reaction is not affected by a Zn2+ ion
chelator and is inhibited by 1 mM Zn2+. With Mg2+ present, the activity is
essentially constant from pH 7 to pH 9.7. pATPase is sensitive to
p-hydroxymercuribenzoate and to N-ethylmaleimide. All four ribonucleoside
triphosphates are hydrolyzed by p action. ATP has the lowest Km (0.009 mM),
while CTP has the highest Vmax. In a mixture containing all four nucleoside
triphosphates at a concentration of 0.4 mM, p shows no strong preference
for any one of the substrates. The response of p ATPase to a variety of
inhibitors of other ATPases and GTPases and of transcription has been
studied. Of the compounds tested, aurintricarboxylic acid, an inhibitor of
protein-nucleic acid interactions, was found to be a potent inhibitor of p
ATPase, while rifampicin and heparin had no effect. pATPase showed partial
sensitivity to thiostrepton, fusidic acid, Dio 9, and sodium azide.