LOCALIZATION OF OCCR-ACTIVATED AND TRAR-ACTIVATED PROMOTERS THAT EXPRESS 2 ABC-TYPE PERMEASES AND THE TRAR GENE OF TI PLASMID PTIR10

Conjugation of Agrobacterium tumefaciens wide-host-range octopine-type Ti plasmids is regulated by the LuxR-type transcriptional activator T raR in conjunction with an acylated homoserine lactone designated AAl. Expression of traR in octopine-type Ti plasmids is stimulated by OccR in response to octopine, an opine released from crown gall tumours, a nd is also positively autoregulated by TraR and AAl. Genetic and physi cal mapping of these promoters indicates that the OccR-activated promo ter lies 14.5 kb upstream of traR, while the TraR-activated promoter l ies 6 kb upstream. The upstream portion of the 14.5 kb operon contains seven previously characterized genes that direct the uptake and catab olism of octopine. The TraR-activated promoter lies just downstream fr om the octopine catabolic genes, and transcribes six genes in addition to traR, including five genes (ophABCDE) that show strong homology to oligopeptide permeases of Salmonella typhimurium and Bacillus subtili s. Several TraR-regulated promoters overlap with 18 bp inverted repeat s called tra boxes. In contrast, the traR autoregulatory promoter is n ot associated with a consensus tra box.