Global transcriptional regulator that complexes with cAMP and binds to specific DNA promoter sites, causing DNA-bending, to regulate transcription. cAMP improves binding to specific DNA sequences, probably by altering protein conformation. The CRP regulon is predicted to contain about 115 genes. Some genes are activated by CRP (rpfA, whiB1) while others are repressed (fadD10). There are 2 CRP-binding sites in the promoter of whiB1, at low concentrations of CRP with or without cAMP transcription of whiB1 is enhanced via site CRP1, then repressed as site CRP2 is filled. Homodimer; in the absence of cAMP the DNA-binding domains are asymmetric in one structure; upon cAMP binding the dimer becomes symmetric, preparing it to bind DNA. Grows more slowly in aerobic liquid culture and on plates, severely impaired growth in unactivated mouse bone marrow-derived macrophages and in infected mice.