Open AccessModE-Dependent Molybdate Regulation of the Molybdenum Cofactor OperonmoainEscherichia coli
Author(s) -
Lisa A. Anderson,
Elizabeth McNairn,
Torben Lübke,
Richard N. Pau,
David H. Boxer
Publication year - 2000
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.182.24.7035-7043.2000
Subject(s) - molybdate , molybdenum cofactor , operon , biology , cofactor , molybdenum , tungstate , sodium molybdate , biochemistry , psychological repression , microbiology and biotechnology , gene , escherichia coli , gene expression , enzyme , chemistry , inorganic chemistry
The expression of themoa locus, which encodes enzymes required for molybdopterin biosynthesis, is enhanced under anaerobiosis but repressed when the bacterium is able to synthesize active molybdenum cofactor. In addition,moa expression exhibits a strong requirement for molybdate. The molybdate enhancement ofmoa transcription is fully dependent upon the molybdate-binding protein, ModE, which also mediates molybdate repression of themod operon encoding the high-affinity molybdate uptake system. Due to the repression ofmoa in molybdenum cofactor-sufficient strains, the positive molybdate regulation ofmoa is revealed only in strains unable to make the active cofactor. Transcription ofmoa is controlled at two sigma-70-type promoters immediately upstream of themoaA gene. Deletion mutations covering the region upstream ofmoaA have allowed each of the promoters to be studied in isolation. The distal promoter is the site of the anaerobic enhancement which is Fnr-dependent. The molybdate induction ofmoa is exerted at the proximal promoter. Molybdate-ModE binds adjacent to the −35 region of this promoter, acting as a direct positive regulator ofmoa . The molybdenum cofactor repression also appears to act at the proximal transcriptional start site, but the mechanism remains to be established. Tungstate in the growth medium affectsmoa expression in two ways. Firstly, it can act as a functional molybdate analogue for the ModE-mediated regulation. Secondly, tungstate brings about the loss of the molybdenum cofactor repression ofmoa . It is proposed that the tungsten derivative of the molybdenum cofactor, which is known to be formed under such conditions, is ineffective in bringing about repression ofmoa . The complex control ofmoa is discussed in relation to the synthesis of molybdoenzymes in the bacterium.