Abstract
The xylABC operon on the TOL plasmid directs the synthesis of enzymes for conversion of toluene to benzoate and is positively controlled by the regulatory gene xylR. In the study here the nucleotide sequence was determined for the regulatory region of this operon. The in vivo transcription initiation site of the operon was determined by S1 nuclease and reverse transcriptase mapping. RNA was prepared from m-methylbenzyl alcohol-induced cells of Pseudomonas putida and Escherichia coli carrying pTN2, a derivative of the TOL plasmid containing the structural and regulatory genes of the entire toluene-degrading pathway. The amount of E. coli mRNA was estimated to be only 10% of that of P. putida mRNA. Consensus sequences of the -10 region (Pribnow box) and the -35 region (RNA polymerase recognition site) in E. coli genes were not found in the region preceding the transcription initiation site, whereas a sequence complementary to the 3' end of the 16S rRNA of Pseudomonas aeruginosa and E. coli existed in front of the predicted start codon of the xylA gene. These results explain the inefficient expression of TOL genes in E. coli.