PLEIOTROPIC EFFECTS OF REGULATORY ROS MUTANTS OF AGROBACTERIUM-RADIOBACTER AND THEIR INTERACTION WITH FE AND GLUCOSE

Four exo mutants of Agrobacterium radiobacter, defective in the synthe sis of acidic exopolysaccharide were complemented by a gene from that species, which is similar to the transcriptional regulator, res, of A, tumefaciens, It was confirmed that this A, radiobacter gene, which we term rosAR, like ras, repressed its own transcription as well as that of virC and virD, two loci involved in tumorigenesis, The sequence of RosAR suggested that it might bind to a transition metal and its repr essor abilities were shown to require Fe in the medium; repression was also enhanced with increasing levels of glucose, Certain rosAR mutant s, in which its 3' end was removed were dominant; i.e. when plasmids c ontaining such mutant forms of the gene were introduced into wild-type A, radiobacter, the transconjugants were nonmucoid, Such effects were also seen in a wide range of bacteria, including Escherichia coli and Xanthomonas. Several mutants that were complemented by rosAR also acc umulated protoporphyrin, suggesting a defect in haem synthesis.