DNA-SEQUENCE AND TRANSCRIPTIONAL ANALYSIS OF THE TBLA GENE REQUIRED FOR TABTOXIN BIOSYNTHESIS BY PSEUDOMONAS-SYRINGAE

The tblA gene of Pseudomonas syringae is required for tabtoxin biosynthesis and is under the control of a regulatory gene, lemA. We have determined the nucleotide sequence of the tblA gene and identified the 5' end of the tblA gene transcript. The sequence of the tbl4 gene was identical to that of the recently reported open reading frame 1 gene of the tabA region of the BR2 chromosome. The open reading frame of the tbl4 gene potentially encodes a protein of 231 amino acids. mRNA from the tbl4 gene was detected at all phases of cells grown in minimal medium. This result is correlated with the constitutive production of tabtoxinine-beta-lactam (the biologically active part of the toxin) by P. syringae BR2R in minimal medium, as quantitated by a phenylisothiocyanate derivatization method.