PROTEIN-PROTEIN COMMUNICATION - STRUCTURAL MODEL OF THE REPRESSION COMPLEX FORMED BY CYTR AND THE GLOBAL REGULATOR CRP

The cAMP receptor protein (CRP) and the Lad-related CytR antiactivator bind cooperatively to adjacent DNA sites at or near promoters, an int eraction that involves direct protein contacts. Here, we identify a co llection of amino acid substitutions in CytR that reestablish protein- protein communication to mutant CRP proteins specifically defective in cooperative binding with wild-type CytR. To assess the location and s patial arrangement of these substitutions, we built a three-dimensiona l model of CytR based on the recent X-ray structure of the highly homo logous PurR repressor bound to DNA. This approach enables us to specif y the patch on CytR's surface that contacts CRP. Furthermore, our resu lts permit the construction of a three-dimensional structure of the hi gher order nucleoprotein complex formed by CytR and CRP.