The Bacillus subtilis tyrS gene belongs to the T box family of aminoacyl-tRNA synthetase and amino acid biosynthesis genes, which are regulated by a common mechanism of transcriptional antitermination. Each gene is induced by specific amino acid limitation; the uncharged cognate tRNA is the effector inducing transcription of the full-length message. The leader regions of the genes in this family share a number of conserved primary sequence and secondary structural elements, the functions of which are unknown. In this study, we examine these regions and report the effects of mutations in several of these elements. In addition, two alternative basepairings in the F box region were found to be necessary for tyrS antitermination.