ATPase associated with ribosomal 30S-5SRNP particles and 40S subunits of rat liver

The ATPase activity of rat liver 30S-5SRNP particles prepared by EDTA treatment of 80S ribosomes, and that of 40S subunits were investigated in correlation with polypeptide elongation. The ATPase activity of 30S-5SRNP particles was higher than that of 40S subunits. Poly(U) and TMV RNA stimulated the ATPase activity of 30S-5SRNP particles more markedly than that of 40S subunits. These two kinds of particles also showed intrinsic GTPase. Poly(U) enhanced the GTPase activity of 30S-5SRNP particles but not that of 40S subunits. An elongation factor (EF-1alpha, EF-2, or EF-1alphabetagamma) alone or in combination with poly(U) and/or other elongation factors stimulated the ATPase activities of both particles. The extent of stimulation of the ATPase activity by a combination of these components was usually somewhat higher than or similar to the sum of those with the individual components. The extents of stimulation by these components were higher in the case of 30S-5SRNP particles than that of 40S subunits, indicating the importance of the 5SRNP moiety in the former particles. The intactness of 18SrRNA was required for promotion of the ATPase activity of 30S-5SRNP particles by Phe(+), (-)tRNA(Phe). The ATPase activities of the two kinds of particles by themselves or those observed with the combinations of the components mentioned above were inhibited by several kinds of translation inhibitors. The degrees of inhibition were generally higher for 30S-5SRNP particles. The ATPase activity of 40S subunits was enhanced by spermidine, suggesting the importance of the conformational change induced by it. These results imply the participation of the intrinsic ATPase of 30S-5SRNP particles and 40S subunits in polypeptide elongation, and the important role of the 5SRNP moiety of 30S-5SRNP particles in the ATPase activity.