Genetic analysis of the modABCD (molybdate transport) operon of XXXX .

@entity535 @entity3782 @entity377 @entity413 @entity5189 @entity526
DNA sequence analysis of the modABCD operon of @entity526 revealed the presence of four open reading frames. The first gene, modA, codes for a 257- @entity535 periplasmic binding protein enunciated by the presence of a signal peptide-like sequence. The second gene (modB) encodes a 229- @entity535 protein with a potential membrane location, while the 352- @entity535 ModC protein (modC product) contains a @entity377 -binding motif. On the basis of sequence similarities with proteins from other transport systems and molybdate transport proteins from other organisms, these three proteins are proposed to constitute the molybdate transport system. The fourth open reading frame (modD) encodes a 231- @entity535 protein of unknown function. Plasmids containing different mod genes were used to map several molybdate-suppressible @entity3782 -resistant mutants; interestingly, none of the 40 mutants tested had a mutation in the modD gene. About 35% of these @entity3782 -resistant mutants were not complemented by mod operon DNA. These mutants, designated mol, contained mutations at unknown chromosomal location(s) and produced @entity5189 hydrogenlyase activity only when cultured in molybdate-supplemented @entity413 -minimal medium, not in L broth. This group of mol mutants constitutes a new class of molybdate utilization mutants distinct from other known mutants in molybdate metabolism. These results show that molybdate, after transport into cells by the ModABC proteins, is metabolized (activated?) by the products of the mol gene(s).
