Identiflcation of clones anE.colitRNAphegene by suppression of pheylananyl-tRNA synthetase thermosensitive mutants

Abstract
Two libraries of cloned E.coli DNA were screened for plasmids which complemented thermosensitive phenylalanyl-tRNA synthetase mutants. Four plasmids were isolated which complemented pheS and pheT thermosen-sitive mutations but which do not carry pheS or pheT, the structural genes for phenylalanyl-tRNA synthetase. All these plasmids increased the intracellular tRNARne concentration. Three plasmids were shown to carry the structural gene for tRNA“ne which we call pheU. By restriction enzyme analysis, DNA blotting and DNA:tRNA hybridization, pheU was localised to a 280 bp fragment within a 5.6 kb PstIrestriction fragment of E.coli DNA.