The catabolite gene activator protein from Klebsiella aerogenes (CAPK) and the corresponding protein from Escherichia coli (CAPE) were shown to be nearly identical. Both CAPK and CAPE activated transcription from the CAP-dependent promoters derived from E. coli and K. aerogenes. The crp gene from K. aerogenes (encoding CAP) is tightly linked to rpsL. The nucleotide sequence of crp predicts an amino acid sequence for CAPK that differs in only one position from that of CAPE.