Two ribonucleic acid-dependent nucleoside triphosphate phosphohydrolases from rat liver nuclei

Two nucleic acid-dependent ATPases have been isolated from hypotonic extracts of rat liver nuclei and partially characterized. Both enzymes are active with RNA and DNA but are most active with RNA. The most abundant enzyme, ATPase I, is a microheterogeneous, monomeric protein that consists of at least three forms with apparent molecular weights from 53,000 to 60,000. It specifically catalyzes the hydrolysis of ATP (or dATP) to ADP (or dADP) and Pi in the presence of Mg2+ ions and nucleic acid cofactor and has a Km for ATP of 0.15 mM. The other enzyme, ATPase II, consists of a single protein with an apparent molecular weight of 37,000. It catalyzes the hydrolysis of all 4 ribonucleoside triphosphates and dATP to the corresponding nucleoside diphosphate and Pi. For both enzymes, nuclear ribonucleoprotein RNA and cytoplasmic poly(A+) RNA are particularly effective cofactors, while total polysomal RNA (primarily rRNA) is a poor cofactor. The properties of these enzymes make them appear similar to other eukaryotic nucleic acid-dependent ATPases that have been isolated but distinct from the prokaryotic enzyme, RNA synthesis termination factor rho. The biological role of these enzymes is unknown.