PROTEIN-PROTEIN INTERACTIONS IN GENE-REGULATION - THE CAMP-CRP COMPLEX SETS THE SPECIFICITY OF A 2ND DNA-BINDING PROTEIN, THE CYTR REPRESSOR

Maximal repression by the CytR protein depends on the formation of nuc leoprotein complexes in which CytR interacts with DNA and with cAMP-cA MP receptor protein (CRP). Here we demonstrate that CytR regulates tra nscription from deoP2 promoters in which the entire CytR recognition s equence has been eliminated. Furthermore, CytR proteins deleted for th e DNA-binding domain repress deoP2 in vivo and interact with deoP2 in vitro in a strictly cAMP-CRP-dependent fashion. These experiments show that the site of action of CytR can be specified by protein-protein i nteractions to cAMP-CRP, whereas CytR-DNA interactions may primarily s erve to stabilize the nucleo-protein complex. This type of specificity mechanism may represent a general concept in the recruitment of DNA-b inding proteins in combinatorial regulatory systems.