MOLECULAR CHARACTERIZATION OF ESCHERICHIA-COLI MALATE SYNTHASE-G - DIFFERENTIATION WITH THE MALATE SYNTHASE-A ISOENZYME

Two genes encoding the enzymes malate synthase G and glycolate oxidase , have been linked to locus glc (64.5 min), responsible for glycolate utilization in Escherichia coli. The gene encoding malate synthase G, for which we propose the notation glcB, has been cloned, sequenced and found to correspond to a 2262-nucleotide open-reading frame, which ca n encode a 723-amino-acid polypeptide, clearly different from the isoe nzyme malate synthase A, which has 533 amino acids. Northern-blot expe riments indicate that glcB was expressed as an apparently monocistroni c transcript, inducible by glycolate. Malate synthase G was purified t o near homogeneity. The molecular mass determined by gel filtration yi elded a value of 82 kDa for the purified enzyme and the same value as for the crude extract enzyme, indicating a monomeric structure. Despit e the lower sequence similarity between malate synthase G and the othe r reported malate synthases, three out of nine consensus boxes defined in most of these enzymes are conserved in addition to a cysteine resi due that has been reported to be important for the catalytic mechanism s.