Structural studies of cytidine repressor and catabolite activator protein

The Escherichia Coli Catabolite Activator Protein (CAP) activates DNA transcription at more than a hundred promoters. Cytidine Repressor (CytR), in conjunction with two CAP dimers, acts as a repressor of DNA transcription at the deoP2 promoter. In the first part of this work, we describe a method by which a (CAP)[subscript] 2-CytR-DNA complex can be prepared for structural studies. In the second part of this project, we describe the crystallization of what was initially intended to be a (CAP)[subscript] 2-DNA complex in order to study the effects of two CAP dimers on transcription at an artificially constructed promoter containing tandem CAP binding sites. Upon structure determination of the crystal, we observed that while there was no DNA present, the protein had bound multiple Co[superscript]2+ and SO2−/4 ligands. We provide an analysis of the crystal structure and present a possible explanation for the absence of DNA in the structure.M.S.Includes bibliographical referencesby Ramya Rangesh Ra