title: A repressor-antirepressor pair links two loci controlling light-induced carotenogenesis in Myxococcus xanthus.
abstract: The light-inducible carB operon encodes all but one of the structural genes for carotenogenesis in Myxococcus xanthus. It is transcriptionally controlled by two proteins expressed from two unlinked genetic loci: CarS from the light-inducible carQRS operon, and CarA from the light-independent carA operon. CarA represses transcription from the carB promoter (P(B)) in the dark, and CarS counteracts this on illumination. The CarA sequence revealed a helix-turn-helix DNA-binding motif of the type found in bacterial MerR transcriptional factors, whereas CarS contains no known DNA-binding motif. Here, we examine the molecular interplay between CarA and CarS. We demonstrate the following. (i) Whereas CarS exhibits no DNA binding in vitro, CarA binds specifically to a region encompassing P(B) to form at least two distinct complexes. (ii) A palindrome located between positions -46 and -63 relative to the transcription start point is essential but not sufficient for the formation of the two CarA-DNA complexes observed. (iii) CarS abrogates the specific DNA binding of CarA. CarA is therefore a repressor and CarS an antirepressor. (iv) CarS physically interacts with CarA; thus, the functional interaction between them is mediated by protein-protein interactions.
authors.affiliation: Departamento de Genética y Microbiología, Facultad de Biología, Universidad de Murcia, Murcia 30071, Spain.
authors.forename: José Juan
authors.initials: JJ
authors.lastname: López-Rubio
authors.forename: Montserrat
authors.initials: M
authors.lastname: Elías-Arnanz
authors.forename: S
authors.initials: S
authors.lastname: Padmanabhan
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Murillo
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites; D002338:Carotenoids / Q000096:biosynthesis*; D002853:Chromatography, Liquid; D004247:DNA / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D008027:Light; D008954:Models, Biological; D008969:Molecular Sequence Data; D016941:Myxococcus xanthus / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques; D014461:Ultracentrifugation
chemical_list: D001426:Bacterial Proteins; C091094:CarS protein, Myxococcus xanthus; D012097:Repressor Proteins; D014157:Transcription Factors; D002338:Carotenoids; D004247:DNA; D003850:Deoxyribonuclease I