MUTANT ALLELES OF TRANSFER RNA(THR) GENES SUPPRESS THE HISG46 MISSENSE MUTATION IN SALMONELLA-TYPHIMURIUM

Extragenic suppressors of the hisG46 missense mutation were mapped to the 71 and 88 min regions of the Salmonella typhimurium chromosome, po sitions that in Escherichia coli contain the thrV (tRNA(Thr1)) and thr T (tRNA(Thr3)) genes, respectively. The suppressor loci were identifie d as mutant alleles of thrV and thrT, using allele-specific colony hyb ridization. An oligomer, based on the conserved 5' sequence of the thr T and thrV genes in E. coli and designed to contain the putative mutan t anticodon, discriminated between suppressor-containing and wild-type strains. Similarly, probes specific for the thrV[SuGGG] and thrT[SuGG G] were used to differentiate the two suppressors. To date, all extrag enic suppressors of hisG46 have been identified as either thrV[SuGGG] or thrT[SuGGG]. A near equal distribution of thrV[SuGGG] and thrT[SuGG G] suppressors was found among 29 spontaneous and 43 mutagen-induced h isG46 extragenic suppressor revertants. It was concluded, therefore, t hat mutant alleles of thrV and thrT are predominantly, if not solely, responsible for intergenic suppression of the hisG46 mutation. (C) 199 4 Wiley-Liss, Inc.