The amino-terminal domain of the prokaryotic enhancer-binding protein XylR is a specific intramolecular repressor.
The mechanism under which the signal-reception amino-terminal portion (A domain) of the prokaryotic enhancer-binding protein XylR controls the activity of the regulator has been investigated through complementation tests in vivo, in which the various protein segments were produced as independent polypeptides. Separate expression of the A domain repressed the otherwise constitutive activity of a truncated derivative of XylR deleted of its A domain (XylR delta A). Such inhibition was not released by m-xylene, the natural inducer of the system. Repression caused by the A domain was specific for XylR because it did not affect activation of the sigma 54 promoter PnifH by a derivative of its cognate regulator, NifA, deleted of its own A domain. The A domain was also unable to repress the activity of a NifA-XylR hybrid protein resulting from fusing two-thirds of the central domain of NifA to the carboxyl-terminal third of XylR, which includes its DNA-binding domain. The inhibitory effect caused by the A domain of XylR on XylR delta A seems, therefore, to result from specific interactions in trans between the two truncated proteins and not from mere hindering of an activating surface.
Pérez-Martín
J
J
Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
De Lorenzo
V
V
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D004268:DNA-Binding Proteins; D004742:Enhancer Elements, Genetic; D004926:Escherichia coli / Q000378:metabolism*; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D008961:Models, Structural; D010446:Peptide Fragments / Q000096:biosynthesis / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis; D014992:Xylenes / Q000494:pharmacology
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C061338:NifA protein, Bacteria; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C074322:XylR protein, Pseudomonas; D014992:Xylenes; D007544:Isopropyl Thiogalactoside; C031285:3-xylene