Catabolite Activator Protein (CAP; also known as cAMP receptor protein, CRP) is a transcriptional activator that exists as a homodimer in solution, with each subunit comprising a ligand-binding domain at the N-terminus (CAP^N, residues 1-138), which is also responsible for the dimerization of the protein, and a DNA-binding domain at the C-terminus (DBD, residues 139-209). Two cAMP (cyclic AMP) molecules bind dimeric CAP with negative cooperativity and function as allosteric effectors by increasing the protein's affinity for DNA. Cytosolic cAMP levels rise when the amount of glucose transported into the cell is low.