Sequence analysis of the upstream region of dhlB, the gene encoding haloalkanoic acid dehalogenase of Xanthobacter autotrophicus GJ10.

The DNA sequence upstream of the dhlB gene encoding the haloalkanoic acid dehalogenase of Xanthobacter autotrophicus GJ10 was determined and contained an open reading frame, designated dhlC, which encoded a protein with a significant similarity with the family of Na(+)-dependent symport proteins. The dhlC gene was subcloned under control of a T7 promoter, and found to encode a polypeptide of 45 kDa on SDS-PAGE. Upstream of dhlC, a -24/-12 promoter sequence was found. Further upstream, in the opposite direction of transcription, another open reading frame, designated dhlR, with homology with the family of sigma 54-dependent transcriptional activator proteins was detected. The dhlR gene was cloned and expressed under the control of a T7 promoter and encoded a polypeptide of 51 kDa on SDS-PAGE. The genetic organization of the dhlB region suggested that the expression of dhlC and dhlB was controlled by the product of dhlR and sigma 54 which may explain the observed overexpression of the haloalkanoic acid dehalogenase under starvation conditions.