Crp of Streptomyces coelicolor is the third transcription factor of the large CRP-FNR superfamily able to bind cAMP.

The chromosomal inactivation of the unique transcription factor of Streptomyces coelicolor that displays a cyclic-nucleotide-binding domain, CrpSco, led to a germination-defective phenotype similar to the mutant of the adenylate cyclase gene (cya) unable to produce cAMP. By means of cAMP affinity chromatography we demonstrate the specific cAMP-binding ability of CrpSco, which definitely demonstrate that a Cya/cAMP/Crp system is used to trigger germination in S. coelicolor. However, electromobility shift assays with the purified CrpSco–cAMP complex and the CRP-like cis-acting element of its own promoter failed. Moreover, we were unable to complement an Escherichia coli crp mutant in trans with CrpSco. The fact that Vfr from Pseudomonas aeruginosa and GlxR from Corynebacterium glutamicum could complement such an E. coli mutant suggests that the way CrpSco interacts with DNA should mechanistically differ from its most similar members. This hypothesis was further supported by homology modelling of CrpSco that confirmed an unusual organisation of the DNA-binding domain compared to the situation observed in CrpEco.