tRNA synthesis: identification of in vivo precursor tRNAs from parental and mutant yeast strains.

In vivo yeast precursor tRNAs have been identified using a modification of the Northern-hybridization procedure. Two species of pre-tRNA Tyr, 1 species of pre-tRNA Ser2 and 2 species of pre-tRNA Serminor have been found in all yeast strains examined, including parental strains and strains harboring mutations affecting tRNA function. One of the tRNA Tyr strains harboring and one of the pre-tRNA SerUCG are the same size as the unspliced pre-tRNAs which accumulate in the yeast mutant rna1. The in vivo tRNA Tyr precursors detected in these studies also appear similar with the RNA species identified when cloned yeast tRNA Tyr is transcribed and processed by Xenopus oocytes and/or Xenopus extracts. We have also studied the precursor and mature tRNA Tyr species from 22 mutants which contain mutations in the SUP4 tyrosine-inserting suppressor locus. The RNA from 2 mutants mapping at the G52 position showing an aberrantly migrating "mature" tRNA Tyr. Although several of those cloned mutant genes showed transcript products of altered size in in vitro transcription studies (1), we did not detect such altered transcripts in vivo.