Analysis of Corynebacterium glutamicum methionine biosynthetic pathway: Isolation and analysis of metB encoding cystathionine gamma-synthase

The metB gene encoding cystathionine gamma-synthase, the second enzyme of m ethionine biosynthetic pathway, was isolated from a pSL109-based Corynebact erium glutamicum gene library via complementation of an Escherichia coli me tB mutant. A DNA-sequence analysis of the cloned DNA identified an open-rea ding frame of 1161 bp which encodes a protein with the molecular weight of 41,655 comprising of 386 amino acids. The putative protein product showed g ood amino acid-sequence homology to its counterpart in other organisms. Int roduction of a plasmid carrying the cloned metB into the C, glutamicum resu lted in a 10-fold increase in cystathionine gamma-synthase activities, demo nstrating the identity of the cloned gene. The C, glutamicum metB mutant wh ich was generated by the site-specific integration of the cloned DNA into i ts chromosome did not lose the ability to grow on glucose minimal medium la cking supplemental methionine. The growth rate of the mutant strain was als o comparable to that of the parental strain. These data indicate that, in a ddition to the transsulfuration pathway, other methionine biosynthetic path ways may be present in C, glutamicum.