Summary: The locus of encodes functions which catalyse the synthesis of active molybdenum cofactor, molybdopterin guanine dinucleotide, from molybdopterin and GTP. Reporter translational fusion mutations in the gene have been constructed using λMu9 mutagenesis. The locus is expressed at very low levels under both aerobic and anaerobic growth conditions. Neither additions to the growth media (nitrate, tungstate or molybdate) nor secondary mutations at the or loci affected the level of expression. Two transcription initiation sites and their associated promoter regions have been identified upstream of . Both of the promoter regions show a poor match to the −35 and −10 consensus sequences for −70 promoters. A 2-2 kb chromosomal DNA fragment which complemented all available mutants has been sequenced. Two ORFs were identified, arranged as a single transcription unit. The encoded polypeptides have predicted molecular masses of 21642 Da and 19362 Da, respectively. The DNA has been subcloned into a T7 overexpression system and the predicted products identified. The gene encodes protein FA, which has been purified to homogeneity and brings about the activation of inactive molybdoenzymes in cell extracts of mutants. The gene encodes a polypeptide with a putative nucleotide binding site. All available mutations which have been selected for by their ability to grow anaerobically in the presence of chlorate are located in the gene.


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