Negative control of octopine degradation and transfer genes of octopine Ti plasmids in Agrobacterium tumefaciens.

The regulatory system that controls the expression of the Ti plasmid-borne octopine degradation (uad) and transfer (tra) genes in Agrobacterium tumefaciens was studied. A deletion mutant derived from the cointegrate plasmid R702::Ti-B6S3 was isolated, which was compatible with a wild-type Ti plasmid and which had retained the uad genes. By means of this mutant plasmid pAL116, it was possible to make cells diploid for the uad genes. pAL116 was introduced into Rec- strains that contained different types of regulation mutants for the uad and tra genes. The repression pattern that was found in this complementation analysis indicated that the uad and tra operons are controlled by a common repressor system. Several results indicated that there may be additional transcriptional relations between both operons. The corresponding genes of the non-tumorigenic octopine plasmid pAt-AG60 appeared to be controlled by a repressor related to that of the octopine Ti plasmid.