The NocR repressor-activator protein regulates expression of thenocBandnocRgenes ofAgrobacterium tumefaciens

摘要

The NocR protein ofAgrobacterium tumefacienswas found to regulate expression of the divergently transcribednocBandnocRgenes of the pTiT37 nopaline catabolism (noc) region. Experiments using the firefly luciferase (luc) gene as reporter demonstrated that NocR represses and activates transcription from thenocBpromoter in the absence and presence of nopaline, respectively. NocR also negatively autoregulates its own synthesis irrespective of the presence of nopaline. Regulation of expression of bothnocBandnocRis mediated by binding of the NocR protein to thenocRpromoter. A 12 by symmetrical sequence, which lies 3 by downstream of the −10 hexamer of thenocRpromoter, was confirmed to be essential for binding of the NocR protein. Functional localization of thenocBandnocRpromoters verified that they do not overlap at all, and that the interrupted dyad, at which NocR binds, is 137 by upstream of the regulatednocBpromoter. The in vivo and in vitro results described here and those published previously suggest that a novel type of regulatory mechanism, which may involve changes in DNA topology, controls gene expression in thenocoperon of pTiT3