CHARACTERIZATION OF PROMOTER RECOGNITION COMPLEXES FORMED BY CRP AND CYTR FOR REPRESSION AND BY CRP AND RNA-POLYMERASE FOR ACTIVATION OF TRANSCRIPTION ON THE ESCHERICHIA-COLI DEOP2 PROMOTER

The structure of the cAMP-CRP-CytR repression complex and the cAMP CRP -RNA polymerase initiation complex at the deoP2 promoter of E. coli ha ve been probed by DNase I and uranyl footprinting. In the CRP2-CytR co mplex all protein DNA-phosphate contacts at CRP-1 and CRP-2 are retain ed, and in addition two new minor groove contacts, ascribed to phospha te-CytR interactions, are observed at -60 between the CRP sites. The c ontacts are compatible with a model in which the promoter DNA is wrapp ed around a complex of two CRPs and one CytR. In the RNA polymerase-CR P complex, the CRP-1 phosphate contacts are almost identical to those seen in the repression complex and strong RNA polymerase contacts are seen in the -10 and in the +10 regions. Most noteworthy are minor groo ve contacts in the -60 region ascribed to RNA polymerase contacts upst ream from the CRP. Furthermore, binding of CRP to the CRP-2 target doe s not seem to interfere with RNA polymerase binding. Thus, a model is suggested in which the DNA is wrapped around a complex of RNA polymera se and one CRP. Finally, the results show that CytR and RNA polymerase are rivals that compete for binding with CRP at deoP2 and that CytR f unctions as an antiactivator.