REGULATION OF CRP TRANSCRIPTION BY OSCILLATION BETWEEN DISTINCT NUCLEOPROTEIN COMPLEXES

FIS belongs to the group of small abundant DNA-binding proteins of Esc herichia coil, We recently demonstrated that, in vivo, FIS regulates t he expression of several genes needed for catabolism of sugars and nuc leic acids, a majority of which are also transcriptionally regulated b y cAMP-cAMP-receptor protein (CRP) complex. Here we provide evidence t hat FIS represses transcription of the crp gene both in vivo and in vi tro, Employing crp promoter-lacZ fusions, we demonstrate that both FIS and cAMP-CRP are required to keep the crp promoter in a repressed sta te. We have identified in the crp promoter other transcription initiat ion sites which are located 73, 79 and 80 bp downstream from the previ ously mapped start site. Two CRP-and several FIS-binding sites with di fferent affinities are located in the crp promoter region, one of them overlapping the downstream transcription initiation sites. We show th at initiation of transcription at the crp promoter is affected by the composition of nucleoprotein complexes resulting from the outcome of c ompetition between proteins for overlapping binding sites. Our results suggest that the control of crp transcription is achieved by oscillat ion in the composition of these regulatory nucleoprotein complexes in response to the physiological state of the cell.