IDENTIFICATION OF AGROBACTERIUM-TUMEFACIENS GENES THAT DIRECT THE COMPLETE CATABOLISM OF OCTOPINE

Agrobacterium tumefaciens R10 was mutagenized by using the promoter pr obe transposon Tn5-gusA7, and a library of approximately 5,000 transcr iptional fusions was screened for octopine-inducible patterns of gene expression, Twenty-one mutants carrying strongly inducible gusA fusion s, 20 of which showed defects in the catabolism of octopine or its met abolites, were obtained, One group of mutants could not use octopine a s a carbon source, while a second group of mutants could not utilize a rginine or ornithine and a third group could not utilize octopine, arg inine, ornithine, or proline as a carbon source, Utilization of these compounds as nitrogen sources showed similar but not identical pattern s, Fifteen fusions were subcloned to ether with adjacent DNA, Sequence analysis and further genetic analysis indicated that insertions of th e first group are localized in the occ region of the Ti plasmid, Inser tions of the second group were localized to a gene encoding ornithine cyclodeaminase. This gene is very similar to, but distinct from, a hom olog located on the Ti plasmid, This gene is located immediately downs tream from a gene encoding an arginase, Genetic experiments indicated that this arginase gene is essential for octopine and arginine catabol ism. Insertions of the third group was localized to a gene whose produ ct is required for degradation of proline, We therefore have identifie d all steps required for the catabolism of octopine to glutamate.