Nucleotide sequence of the regulatory gene xylR of the TOL plasmid from Pseudomonas putida

We have determined the nucleotide sequence of the xylR gene for a transcriptional activator for the degradative pathway of aromatic hydrocarbons on the TOL plasmid from Pseudomonas putida. The 1698-bp sequence for a 566-amino acid (aa) protein (Mr 63741) was identified as the XylR-encoding sequence. Three regions in XylR show homology to Klebsiella pneumoniae NtrC and NifA, both of which are transcriptional activators for the ntr and nif genes involved in the nitrogen metabolism. The central region of XylR (aa 234-473) corresponds to the region that was proposed to interact with RNA polymerase having a sigma factor, NtrA [Drummond et al., EMBO J. 5 (1986) 441-447]. The C-terminal region (aa 515-558) has a putative DNA-binding structure. A short segment proximal to the central region (aa 211-229) is thought to be an interdomain linker. No amino acid homology was found in the N-terminal regions among these proteins. These findings suggest the interaction of XylR with an NtrA in the transcriptional activation of the degradative pathway.