PHYSIOLOGICAL AND GENETIC ANALYSES LEADING TO IDENTIFICATION OF A BIOCHEMICAL ROLE FOR THE MOEA (MOLYBDATE METABOLISM) GENE-PRODUCT IN ESCHERICHIA-COLI

A unique class of chlorate-resistant mutants of Escherichia coli which produced formate hydrogenlyase and nitrate reductase activities only when grown in medium with limiting amounts of sulfur compounds was iso lated. These mutants failed to produce the two molybdoenzyme activitie s when cultured in I ich medium or glucose-minimal medium, The mutatio ns in these mutants were localized in the moeA gene, Mutant strains wi th polar mutations in moeA which are also moeB did not produce active molybdoenzymes in any of the media tested. moeA mutants with a second mutation in either cysDNCJI or cysH gene lost the ability to produce a ctive molybdoenzyme even when grown in medium limiting in sulfur compo unds, The CysDNCJIH proteins along with CysG catalyze the conversion o f sulfate to sulfide. Addition of sulfide to the growth medium of moeA cys double mutants suppressed the MoeA(-) phenotype. These results su ggest that in the absence of MoeA protein, the sulfide produced by the sulfate activation/reduction pathway combines with molybdate in the p roduction of activated molybdenum. Since hydrogen sulfide is known to interact with molybdate in the production of thiomolybdate, it is poss ible that the MoeA-catalyzed activated molybdenum is a form of thiomol ybdenum species which is used in the synthesis of molybdenum cofactor from Mo-free molybdopterin.