Stimulation of an Artemia salina ATPase activity by eukaryotic messenger RNAs

An RNA-dependent nucleoside triphosphate hydrolase from Krebs-II ascites tumor cells. Detection and preliminary characterization

A novel enzymatic activity, RNA-dependent, NTPase, was isolated from Krebs-II ascites tumor cells. This activity is associated with ribosomes and can be detached from them by washing in KCl solutions of a higher than 0.3 M concentration. The enzyme hydrolyzes all the four nucleoside triphosphates to the corresponding nucleoside diphosphates and orthophosphate. The rate of NTP hydrolysis increases about 10-fold in the presence of natural RNAs and synthetic polyribonucleotides [except poly(G)]. Natural DNAs, both double and single-stranded, are poor cofactors, although pol(dA) and poly(dT) stimulate, to a certain extent, the rate of ATP hydrolysis. Possible involvement of RNA-dependent NTPase in protein biosynthesis is discussed.

An RNA-dependent ATPase from Chlamydomonas reinhardII

An RNA-dependent ATPase has been isolated from extracts of Chlamydomonas reinhardii. The enzyme catalyzes the hydrolysis of ATP, dATP, CTP and dCTP to the corresponding nucleoside diphosphate and Pi in the presence of Mg2+ or Mn2+ and an RNA cofactor. In 1 mM MgCl2 it displays the greatest activity with poly(A), poly(I) and poly(U); and somewhat lower activity with poly(C) and T7 RNA. Although the enzyme is active with single-stranded DNA, all the single-stranded RNAs tested were significantly more effective cofactors than any of the single or double-stranded DNAs tested. A comparison of this ATPase with other RNA-dependent ATPases indicates that is has more in common with the ATPase isolated from the nuclei of animal cells than with the RNA synthesis termination protein rho, the major RNA-dependent ATPase from Escherichia coli. Although chloroplasts of C. reinhardii are known to contain many bacterial-like gene expression components, the presence of an enzyme with close homology to the E. coli rho protein was not detected.