Opine transport genes in the octopine (occ) and nopaline (noc) catabolic region in Ti plasmids of Agrobacterium tumefaciens

The occ and noc regions of octopine and nopaline Ti plasmids in Agrobacterium tumefaciens are responsible for the catabolic utilization of octopine and nopaline, respectively. Opine-inducible promoters, genes for regulatory proteins and for catabolic enzymes, had been identified in previous work. However, both regions contained additional DNA stretches which were under the control of opine-inducible promoters, but the functions were unknown. We investigated these stretches by DNA sequence and functional analyses. The sequences showed that both of the catabolic regions contain a set of four genes which are transcribed in the same direction. The occ and noc region genes are related, but the arrangement of the genes is different. The deduced polypeptides are related to those of binding protein-dependent transport systems of basic amino acids in other bacteria. The comparison suggested that three of the polypeptides are located in the membrane and that one is a periplasmic protein. We constructed cassettes which contained either the putative transport genes only or the complete occ or noc region; all constructs, however, included the elements necessary for opineinduced expression of the genes (the regulatory gene and the inducible promoters). Uptake studies with 3H-labelled octopine showed that the putative transport genes in the occ region code for octopine uptake proteins. The corresponding studies with 3H-labelled nopaline and the noc region cassettes indicated that the uptake of nopaline requires the putative transport genes and additional functions from the left part of the noc region. Plant tumors induced by Agrobacterium tumefaciens synthesize a group of substances (opines) which are metabolized by the bacteria. This is an important part of the interaction with plants and presumably was the driving force in the evolution of the systems (10). The genes that are essential for opine catabolism are located on the Ti plasmids. In the case of nopaline and octopine plasmids, the regions are called the occ and noc regions, respectively. Ti plasmids with the occ region confer octopine [N2-(1-Dcarboxyethyl)-L-arginine] but not nopaline [N2-(1,3-D-dicar