title: Transcriptional regulation of molybdoenzyme synthesis in Escherichia coli in response to molybdenum: ModE-molybdate, a repressor of the modABCD (molybdate transport) operon is a secondary transcriptional activator for the hyc and nar operons.
abstract: Escherichia coli growing under anaerobic conditions produces several molybdoenzymes, such as formate hydrogenlyase (formate to H2 and CO2; hyc and fdhF genes) and nitrate reductase (narGHJI genes). Synthesis of these molybdoenzymes, even in the presence of the cognate transcriptional activators and effectors, requires molybdate in the medium. Besides the need for molybdopterin cofactor synthesis, molybdate is also required for transcription of the genes encoding these molybdoenzymes. In E. coli, ModE was previously identified as a repressor controlling transcription of the operon encoding molybdate transport components (modABCD). In this work, the ModE protein was also found to be a required component in the activation of hyc-lacZ to an optimum level, but only in the presence of molybdate. Mutant ModE proteins which are molybdate-independent for repression of modA-lacZ also restored hyc-lacZ expression to the wild-type level even in the absence of molybdate. Nitrate-dependent enhancement of transcription of narX-lacZ was completely abolished in a modE mutant. Nitrate-response by narG-lacZ and narK-lacZ was reduced by about 50% in a modE mutant. DNase I footprinting experiments revealed that the ModE protein binds the hyc promoter DNA in the presence of molybdate. ModE-molybdate also protected DNA in the intergenic region between narXL and narK from DNase I hydrolysis. DNA sequences (5' TAYAT 3' and 5' GTTA 3') found in ModE-molybdate-protected modABCD operator DNA were also found in the ModE-molybdate-protected region of hyc promoter DNA (5' GTTA-7 bp-CATAT 3') and narX-narK intergenic region (5' GTTA-7 bp-TACAT 3'). Based on these results, a working model is proposed in which ModE-molybdate serves as a secondary transcriptional activator of both the hyc and narXL operons which are activated primarily by the transcriptional activators, FhlA and NarL, respectively.
authors: William T
authors: WT
authors: Self
authors: Amy M
authors: AM
authors: Grunden
authors: Adnan
authors: A
authors: Hasona
authors: K T
authors: KT
authors: Shanmugam
mesh_terms: D027321:Anion Transport Proteins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics; D018983:DNA Footprinting; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins; D005560:Formate Dehydrogenases / Q000235:genetics; D005561:Formates / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D017930:Genes, Reporter; D006864:Hydrogenase / Q000235:genetics; D008667:Metalloproteins / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000378:metabolism / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000235:genetics; D009154:Mutation; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism; D009876:Operon; D011401:Promoter Regions, Genetic / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005561:Formates; D008667:Metalloproteins; C491064:ModE protein, E coli; C101050:ModE protein, bacteria; D009097:Multienzyme Complexes; D000091285:Nitrate Transporters; D009566:Nitrates; D014157:Transcription Factors; C030544:formic acid; C069780:NarL protein, E coli; C044659:molybdate; D008982:Molybdenum; C031618:sodium nitrate; D006864:Hydrogenase; D005560:Formate Dehydrogenases; C054017:formate hydrogenlyase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D011494:Protein Kinases; C074787:narX protein, E coli