OPINE-REGULATED PROMOTERS AND LYSR-TYPE REGULATORS IN THE NOPALINE (NOC) AND OCTOPINE (OCC) CATABOLIC REGIONS OF TI PLASMIDS OF AGROBACTERIUM-TUMEFACIENS

Essential steps in the uptake and catabolism of the plant tumor metabo lites nopaline and octopine in Agrobacterium spp. are performed by pro teins encoded in the nopaline catabolic (noc) and octopine catabolic ( occ) regions of Ti plasmids. We investigated the opine activation of t he genes by using (i) promoter studies of Agrobacterium spp. and (ii) analysis of the promoter interaction with the regulatory proteins NocR (noc) and OccR (occ). The noc region contained two nopaline-induced p romoters (Pi1[noc] and Pi2[noc]) and one autogenously regulated promot er (Pr [control of NocR expression]). Pi2 and Pr overlapped and were d ivergently oriented (Pi2/Pr[noc]). DNA binding studies and DNase I foo tprints indicated that NocR bound specifically to single binding sites in Pi1[noc] and Pi2/Pr[noc] and that Pi2 and Pr were regulated from t he same binding site. The binding was independent of the inducer nopal ine, and nopaline caused small changes in the footprint. The promoters in the noc and occ regions shared sequence motifs and contained the s equence T-N11-A, which is characteristic for LysR-type-regulated promo ters. The occ region contained one octopine-induced and one autogenous ly regulated promoter (Pi/Pr[occ]) in the same arrangement as Pi2/Pr[n oc] in the noc region. Promoter deletions indicated that sequences fla nking the OccR binding site determined the extent of induction, althou gh they did not bind OccR. The promoter bound OccR in the absence and presence of octopine. The opine caused a change in the mobility of the DNA-protein complex with the complete promoter. The resected fragment s did not reveal this opine-induced shift, and it was also not detecta ble with the DNA-NocR complexes with the two promoters of the noc regi on.