MUTATIONS IN THE GENE FOR A TRANSFER-RNA 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 i n Bacillus subtilis and related bacteria by interacting with leader se quences to cause antitermination. In this study we report the isolatio n and characterization of regulatory mutations that modify one of the tRNA molecules predicted to have such a regulatory role. Three differe nt alleles of the B. subtilis leucine tRNA gene leu G 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 tRP\JA molecul e with the anticodon 5'-GAG-3' (leucine tRNA(GAG)). Experiments with s trains that are diploid for mutant and wild-type alleles suggested tha t both charged and uncharged tRNA molecules may interact with leader s equences to control expression of the operon.