HOMOLOGY OF PYRIDOXAL-5'-PHOSPHATE-DEPENDENT AMINOTRANSFERASES WITH THE COBC (COBALAMIN SYNTHESIS), NIFS (NITROGEN-FIXATION), PABC (P-AMINOBENZOATE SYNTHESIS) AND MALY (ABOLISHING ENDOGENOUS INDUCTION OF THE MALTOSE SYSTEM) GENE-PRODUCTS

Bacterial deletion mutants have indicated that the gene products of cobC, nifS, pabC and malY participate in important metabolic pathways, i.e. cobalamin synthesis, nitrogen fixation, synthesis of p-aminobenzoate and the regulation of the maltose system, respectively. However, the proteins themselves and their specific functions have not yet been identified. In the course of our studies on the evolutionary relationships among aminotransferases, we have found that the above gene products are homologous to aminotransferases. Profile analysis [Gribskov, M., Luthy, R. & Eisenberg, D. (1990) Methods Enzymol. 183, 146-159] based on the amino acid sequences of certain subgroups of aminotransferases as probes attributed significant Z scores in the range 5-20 SD to the deduced amino acid sequences of the above gene products as included in the protein data base. Reciprocal profile analyses confirmed the homologies. All known aminotransferases are pyridoxal-5'-phosphate-dependent enzymes and catalyze the reversible transfer of amino groups from amino acids to oxo acids. The sequence homologies suggest that the above gene products are aminotransferases or other closely related pyridoxal-5'-phosphate-dependent enzymes probably catalyzing transformations of amino acids involving cleavage of a bond at Calpha.