Analysis of the 5′ regulatory region of the gene for δ-aminolevulinic acid synthetase ofRhizobium meliloti

Open Access
Publisher Website
Google Scholar
Abstract
Transcriptional regulation of the δ-aminolevulinic acid synthetase gene of Rhizobium meliloti was investigated under conditions of nornal vegetative growth and during symbiosis with the legume host alfalfa. S1 nuclease mapping and DHA sequence analysis indicated that transcription originates from two sites separated by 238 base pairs. A deletion analysis of the putative promoter regions P1 and P2, corresponding to the proximal and diatal RNA start sites, was carried out with Bal-31 nuclease. Promoter function was monitored as β-galactosidase activity after fusing the deletions to lac Z and introducing them into Rhizobium on a broad host range plasmid. The data obtained suggest that both regions function equivalently as promoters. The DNA sequences of P1 and P2 show considerable homology in the region between −35 and the start of transcription. Both contain a −35 region that is analogous to the consensus E. coli promoter sequence, while the −10 region is dissimilar. No resemblance was found between either P1 or P2 and the promoter regions of genes under general nitrogen control.