Mutations in the gene for a tRNA that functions as a regulator of a transcriptional attenuator in Bacillus subtilis

It has been proposed that uncharged tRNA molecules may act as positive regulatory factors to control the expression of a number of operons in Bacillus subtilis and related bacteria by interacting with leader sequences to cause antitermination. In this study we report the isolation and characterization of regulatory mutations that modify one of the tRNA molecules predicted to have such a regulatory role. Three different alleles of the B. subtilis leucine tRNA gene leuG were found that resulted in higher expression of the ilv-leu biosynthetic operon. Each resulted in a base change in the D-loop of the leucine tRNA molecule with the anticodon 5'-GAG-3' (leucine tRNAGAG). Experiments with strains that are diploid for mutant and wild-type alleles suggested that both charged and uncharged tRNA molecules may interact with leader sequences to control expression of the operon.