ANALYSIS OF THE BACILLUS-SUBTILIS TYRS GENE - CONSERVATION OF A REGULATORY SEQUENCE IN MULTIPLE TRANSFER-RNA SYNTHETASE GENES

The Bacillus subtilis tyrS gene, which encodes tyrosyl-tRNA synthetase (TyrTS), was isolated, and its nucleotide sequence was determined. The cloned gene was shown to complement an Escherichia coli tyrS(Ts) mutant. The predicted amino acid sequence exhibited 70% identity to that of Bacillus stearothermophilus TyrTS and 55% identity to that of E. coli TyrTS, while identity to a second cryptic B. subtilis TyrTS gene, designated tyrZ, was only 27%. Primer extension analysis indicated that tyrS transcription initiated at a vegetative promoter sequence located 300 nucleotides upstream of the AUG start codon. The mRNA leader region was found to contain an inverted repeat sequence resembling a transcriptional terminator. Expression of a transcriptional tyrS-lacZ found to be induced by starvation for tyrosine in a tyrosine auxotroph (tyrA1). Transcription initiation was unaffected by tyrosine starvation. Deletion of the terminator region in a tyrS-lacZ fusion resulted in high-level constitutive expression. Immediately preceding the putative terminator was a sequence element found to be conserved in the upstream region of a number of Bacillus tRNA synthetase genes as well as in the ilv-leu biosynthetic operon; mutation of this element in tyrS resulted in low-level uninducible expression. The conservation of this sequence element suggests that aminoacyl-tRNA synthetase genes and the ilv-leu operon may be regulated by a common mechanism in Bacillus spp.