Partial characterization of the ribonuclease P from Tetrahymena pyriformis.
Ribonuclease P activity from infusoria Tetrahymena pyriformis has been isolated and purified more than 1000-fold over cytosol crude extract. Purified tRNA 5' endonuclease processes in vitro heterologous substrates, precursors of the human tRNA(Tyr) and Drosophila melanogaster tRNA(Leu), exactly at the 5' end of the mature molecules. The activity was abolished by micrococcal nuclease and protease treatment indicating that both RNA and protein components are essential for its activity. The most abundant polypeptides in the purified enzyme fractions have molecular masses of about 100, 44 and 35 kDa. The enzyme requires divalent cations for its activity and shows optimal activity in the presence of the low concentrations of the monovalent salts. Substrate structural requirements for the purified enzyme were analyzed with different tRNA precursor models. The analysis of the derivatives of tRNA(Leu) precursors with altered aminoacyl stem structures reveals that end of the stem is important for substrate 5' end processing with purified enzyme.