Normal and mutant glycine transfer RNAs.

Abstract

THE glycine-specific tRNAs of E. coli can be grouped into three subspecies which are separated by chromatography on benzoylated DEAE cellulose (BDC): tRNAGly1 (GGG), tRNAGly2 (GGA/G) and tRNAGly3 (GGU/C)1,2. The tRNAGly1 and tRNAGly2 are specified by the genes, glyU and glyT, respectively, which have been located at 55 and 77 minutes on the E. coli chromosome. Suppressors of tryptophan A gene (trpA) missense mutations and partial diploid strains have been used extensively to characterize the glycine tRNA structural genes (Table 1)1–3. A common property of these suppressor mutations is that the altered tRNAGly is no longer aminoacylated at the normal rate by the glycyl tRNA synthetase (GRS). When ordinary loading conditions are used virtually none of the suppressor tRNA species are amino-acylated. These studies have shown that single gene copies are normally present at the glyT and glyU loci.