Insertion (sufB) in the anticodon loop or base substitution (sufC) in the anticodon stem of tRNA(Pro)2 from Salmonella typhimurium induces suppression of frameshift mutations.

The dominant +1 frameshift suppressors sufA6, sufB1 and sufB2, in Salmonella typhimurium act at runs of C and affect tRNA(Pro)1, tRNA(Pro)2 and tRNA(Pro)2, respectively. A recessive +1 frameshift suppressor, sufC, has a similar suppressor specificity (Riddle, D.L., and Roth, J.R., Mol. Biol. 66, 483 and 495, 1972). We show that sufC strains harbour two frameshift suppressors of which one, sufX201, is allelic to sufB. We cloned the sufB+ wild type allele and by recombination in vivo the mutations sufB1, sufB2 and sufX201. Determination of the DNA sequence revealed that the sufB1 and sufB2 mutations result in an extra G in the anticodon loop of the minor tRNA(Pro)2. The sufX201 mutation results in a base substitution (G43 to A43) in the anticodon stem of this tRNA. Although the sufB1 and sufB2 mutations were earlier shown to be dominant, the sufB+ wild type allele on multi copy plasmid inhibited the chromosomal sufB1, sufB2 and sufX201 mediated frameshift suppression but not that mediated by the dominant sufA6 mutation. These results are discussed in view of the possible coding specificity of these mutated tRNAs. The DNA sequence showed a potential consensus promoter sequence upstream of the structural gene for tRNA(Pro)2 and downstream a dyad symmetrical structure followed by a T cluster, a possible rho-independent termination signal. The Salmonella tRNA(Pro)2 gene is identical to the Escherichia coli counterpart reported by Komine, Y. et al. (J. Mol. Biol. 212, 579-598, 1990). While the 5' flanking sequence similarity between the two species is about 83%, the similarity of the 3' flanking sequence is only 42%. Still, the Salmonella tRNA(Pro)2 gene has a rho-independent transcriptional termination signal similar to the one present in E. coli tRNA(Pro)2 gene.