TRNA SYNTHESIS IN HELA CELLS - A PRECURSOR TO TRNA AND EFFECTS OF METHIONINE STARVATION ON TRNA SYNTHESIS

A class of small RNA molecules which migrates slower than tRNA during gel electrophoresis has been shown to be in all likelihood a precursor to tRNA. This species, termed pre-tRNA, is labeled by uridine before tRNA; in the presence of actinomycin, labeled pre-tRNA disappears and radioactivity appears in tRNA. Pre-tRNA is methylated and its apparent conversion to tRNA is slowed during starvation for methionine, the methyl donor for RNA methylation. During methionine starvation the methyl acceptor activity in tRNA rises although pre-tRNA does not accumulate. It therefore appears that pre-tRNA can be changed so that it migrates with tRNA without being completely methylated. Because pre-tRNA can not be made to migrate with tRNA by treatments known to destroy all secondary structure in tRNA, it is suggested that pre-tRNA may be longer than tRNA and the methyl-dependent step might be a nuclease attack at a specific site. © 1969.