Role of 5SrRNA as a Positive Effector of Some Aminoacyl-tRNA Synthetases in Macromolecular Complexes, with Specific Reference to Methionyl-tRNA Synthetase

Abstract

1) Rat liver 5SrRNA enhanced the activity of methionyl-tRNA synthetase in the macromolecular aminoacyl-tRNA synthetase complex (Fraction B) purified from a rat liver supernatant. 5SrRNA-L5 protein complexes (5SrRNP) had similar effects, whereas other ribosomal RNAs and E. colt 5SrRNA had no effect. 2) 5SrRNA increased the activity of the complex for methionine-dependent ATP-PP₁ exchange. 3) 5SrRNA increased the activities of methionyl-, arginyl-, and isoleucyl-tRNA synthetases in the complex, but scarcely affected its leucyl-, lysyl-, and glutamyl-tRNA synthetase activities. 4) 5SrRNA increased the activities of the rat liver supernatant for the attachment of [³⁵S]methionine, [³H] isoleucine, [³H]lysine, [³H]proline, [³H]threonine, [³H] tyrosine, and [³H]phenylalanine to endogenous tRNA markedly, and those for [³H]leucine, [³H]arginine, [³H]aspartic acid, and [3H]histidine slightly, but did not affect those for [³H] glutamic acid, [³H] glycine, [³H] valine, [³H] alanine, and [³H] tryptophan. 5) Preincubation of the rat liver supernatant with an antibody against Artemia salina ribosomal protein L5, that cross-reacted with the rat liver ribosomal protein L5, decreased the attachment of [³⁵S]methionine and [³H]-isoleucine to endogenous tRNA, and 5SrRNA and 5SRNP enhanced these activities of the supernatant preincubated with antibody. On the other hand, the antibody did not affect that for [³H]alanine. Immune dot blot analysis using the antibody against L5 showed the presence of immunologically the same protein as L5 in the liver supernatant. Northern blot analysis of RNA in the immunoprecipitate prepared from the liver supernatant incubated with the antibody against L5 indicated that 5SrRNA was complexed with L5. These results together with those of previous experiments indicate that 5SrRNA, which may be present as 5SrRNA, plays a role as a positive effector of methionyl- and isoleucyl-tRNA synthetases in the macromolecular aminoacyl-tRNA synthetase complex.