Molecular Characterization of AceB, a Gene Encoding Malate Synthase in Corynebacterium glutamicum

The aceB gene, encoding for malate synthase, one of the key enzymes of glyoxylate bypass, was isolated from a pMT1-based Corynebacterium glutamicum gene library via complementation of an Escherichia coli aceB mutant on an acetate minimal medium. The aceB gene was closely linked to aceA, separated by 598 base pairs, and transcribed in divergent direction. The aceB expressed a protein product of Mr 83, 000 in Corynebacterium glutamicum which was unusually large compared with those of other malate synthases. A DNA-sequence analysis of the cloned DNA identified an open-reading frame of 2, 217 base pairs which encodes a protein with the molecular weight of 82, 311 comprising 739 aminoo acids. The putative protein product showed only limited amino acid-sequence homology to its counteliparts in other organisms. The N-terminal region of the protein, which shows no apparent homology with the known sequences of other malate synthases, appeared to be responsible for the protein s unusually large size. A potential calciumbinding domain of EF-hand structure found among eukaryotes was detected in the N-terminal region of the deduced protein.