Catabolite Activator Protein (also known as cAMP receptor protein, CRP) activates transcription of more than a hundred promoters, allowing for synthesis of various enzymes required for degradation of non-glucose molecules. Structurally, it forms a homodimer with a DNA binding site, a cyclic adenosine monophosphate (cAMP), and an RNA polymerase. The cAMP acts as an allosteric regulator to activate CAP, promoting expression of metabolic genes. For example, in bacteria (such as E. coli), the CAP activation is essential for Lac operon expression, allowing for production of β-galactosidase, an enzyme that breaks down milk sugar (lactose to make it available for cellular energy metabolism.