Mutant alleles of tRNAThr genes suppress the hisG46 missense mutation in Salmonella typhimurium

Abstract

Extragenic suppressors of the hisG46 missense mutation were mapped to the 71 and 88 min regions of the Salmonella typhimurium chromosome, positions that in Escherichia coli contain the thrV (tRNA^Thr1) and thrT (tRNA^Thr3) genes, respectively. The suppressor loci were identified as mutant alleles of thrV and thrT, using allelespecific colony hybridization. An oligomer, based on the conserved 5′ sequence of the thrT and thrV genes in E. coli and designed to contain the putative mutant anticodon, discriminated between suppressor‐containing and wild‐type strains. Similarly, probes specific for the thrV‐[SuGGG] and thrT[SuGGG] were used to differentiate the two suppressors. To date, all extragenic suppressors of hisG46 have been identified as either thrV[SuGGG] or thrT[SuGGG]. A near equal distribution of thrV[SuGGG] and thrT[SuGGG] suppressors was found among 29 spontaneous and 43 mutagen‐induced hisG46 extragenic suppressor revertants. It was concluded, therefore, that mutant alleles of thrV and thrT are predominantly, if not solely, responsible for intergenic suppression of the hisG46 mutation. © 1994 Wiley‐Liss, Inc.^†