The Noc region of Ti plasmid C58 codes for arginase and ornithine cyclodeaminase

Plant tumors induced by Agrobacterium tumefaciens synthesize a group of substances (opines) which can serve as sole source of carbon and nitrogen for the bacteria. We investigate Ti-plasmid-coded genes and enzymes involved in catabolism of the opine N2-(1,3-dicarboxypropyl)-L-arginine (nopaline) with a novel approach: expression and mapping of protein-coding regions in Escherichia coli minicells, followed by identification of enzyme functions in the heterologous E. coli background. The results show that a specific part of the nopaline catabolism (Noc) region of Ti plasmid C58 is packed with closely spaced protein-coding regions which can be expressed into polypeptides of distinct sizes in E. coli. We identify and map three enzyme activities: nopaline oxidase, arginase and ornithine cyclodeaminase, an unusual protein converting ornithine directly into proline. Nopaline oxidase requires two different Noc-gene-encoded proteins for function and the latter two enzymes are new discoveries in the Noc region. These three enzyme activities together constitute a catabolic pathway leading from nopaline through arginine and ornithine to proline.