Structure of PrfA (A) and its target DNA sequences in PrfA-regulated promoters (B). Structure of PrfA (A) and its target DNA sequences in PrfA-regulated promoters (B). See text for details. In PrfA, amino acid coordinates correspond to the peptide sequence deduced from theprfA gene (position 1 corresponds to the Met residue of the first triplet), whereas in Crp they correspond to the actual amino acid position in the primary structure of the native protein, which lacks the residue encoded by the first triplet. Therefore, the amino acid numbering of Crp is shifted one position with respect to that of PrfA, and hence, position 144 of Crp, where the Crp* mutation Ala→Thr lies, aligns exactly with position 145 of PrfA, where the Gly→Ser substitution leading to the PrfA* mutant phenotype is located. In Crp, A to F designate the α-helical stretches of the protein and AR1 is activating region 1 (two other activating regions [AR2 and AR3] are embedded within the β-roll structure). In PrfA, structures specific for this protein are in light gray. (B) N indicates any nucleotide. (Adapted from references 66 and 221.)‏ José A. Vázquez-Boland et al. Clin. Microbiol. Rev. 2001; doi:10.1128/CMR.14.3.584-640.2001