MUTATIONS IN THE CORYNEBACTERIUM-GLUTAMICUM PROLINE BIOSYNTHETIC-PATHWAY - A NATURAL BYPASS OF THE PROA STEP

Two chromosomal loci containing the Corynebacterium glutamicum ATCC 17 965 proB and proC genes were isolated by complementation of Escherichi a coil proB and proC auxotrophic mutants, Together with a proA gene de scribed earlier, these new genes describe the major C. glutamicum prol ine biosynthetic pathway, The proB and proA genes, closely linked in m ost bacteria, are in C. glutamicum separated by a 304-amino-acid open reading frame (unk) whose predicted sequence resembles that of the 2-h ydroxy acid dehydrogenases. C. glutamicum mutants that carry null alle les of proB, proA, and proC were constructed or isolated from mutageni zed cultures, Single proC mutants are auxotrophic for proline and secr ete Delta(1)-pyrroline-5-carboxylate, which are the expected phenotype s of bacterial proC mutants, However, the phenotypes of proB and proA mutants are unexpected, A proB mutant has a pleiotropic phenotype, bei ng both proline auxotrophic and affected in cell morphology. Null proA alleles still grow slowly under proline starvation, which suggests th at a proA-independent bypass of this metabolic step exists in C. gluta micum, Since proA mutants are complemented by a plasmid that contains the wild-type asd gene of C. glutamicum, the asd gene may play a role in this bypass.