T box sequences have been identified upstream of a large number of uncharacterized genes such as transporters in bacterial genomes. Expression of each T box family gene is induced by limitation for a specific amino acid. T box family genes contain an untranslated leader region containing a factor-independent transcriptional terminator upstream of the structural genes. The anticodon of uncharged tRNA base-pairs with the leader mRNA at a codon referred to as the specifier sequence, inducing formation of an alternative antiterminator structure, allowing expression of the structural genes. There are several additional conserved primary sequence and secondary structural elements. Analysis of these elements can be used to predict the identity of the specifier codon and the amino acid signal. Bacillus subtilis hypothetical amino acid permease, yvbW, was analyzed as an example of this type of transcriptional regulatory prediction suggesting expression in response to leucine limitation. Expression was induced up to 130-fold in response to leucine limitation, utilizing a yvbW-lacZ transcriptional fusion. These data suggest that hypothetical amino acid permease YvbW may participate in leucine metabolism. A yvbW knockout strain was generated, although the substrate specificity for the putative amino acid permease was not identified.