A BACTERIAL BASIC REGION LEUCINE-ZIPPER HISTIDINE KINASE REGULATING TOLUENE DEGRADATION

The two-component signal transduction pathways in bacteria use a histi dine-aspartate phosphorelay circuit to mediate cellular changes in res ponse to environmental stimuli, Here we describe a novel two-component todST system, which activates expression of the toluene degradation ( tod) pathway in Pseudomonas putida F1. The todS gene is predicted to e ncode a sensory hybrid kinase with two unique properties-a basic regio n leucine zipper dimerization motif at the N terminus and a duplicated histidine kinase motif. Evidence from a synthetic peptide model sugge sts that TodS binds as a dimer to a pseudopalindromic sequence (5'-TGA CTCA), which resembles the recognition sequence of the eukaryotic tran scription factors Fos and Jun, These results provide additional eviden ce that bacteria and eukaryotes share common regulatory motifs, The to dT gene product, a response regulator, was overproduced as a fusion pr otein in Escherichia coli, and the purified protein was found to bind specifically to a 6-bp palindromic DNA structure in the rod control re gion, The phosphorylated form of TodT appears to be the activator of t od structural genes, This is the first report of a two-component syste m that regulates aromatic metabolism in bacteria.