S. Ankri et al., MUTATIONS IN THE CORYNEBACTERIUM-GLUTAMICUM PROLINE BIOSYNTHETIC-PATHWAY - A NATURAL BYPASS OF THE PROA STEP, Journal of bacteriology, 178(15), 1996, pp. 4412-4419
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.