title: Nucleotide sequence of the colicin B activity gene cba: consensus pentapeptide among TonB-dependent colicins and receptors.
abstract: Colicin B formed by Escherichia coli kills sensitive bacteria by dissipating the membrane potential through channel formation. The nucleotide sequence of the structural gene (cba) which encodes colicin B and of the upstream region was determined. A polypeptide consisting of 511 amino acids was deduced from the open reading frame. The active colicin had a molecular weight of 54,742. The carboxy-terminal amino acid sequence showed striking homology to the corresponding channel-forming region of colicin A. Of 216 amino acids, 57% were identical and an additional 19% were homologous. In this part 66% of the nucleotides were identical in the colicin A and B genes. This region contained a sequence of 48 hydrophobic amino acids. Sequence homology to the other channel-forming colicins, E1 and I, was less pronounced. A homologous pentapeptide was detected in colicins B, M, and I whose uptake required TonB protein function. The same consensus sequence was found in all outer membrane proteins involved in the TonB-dependent uptake of iron siderophores and of vitamin B12. Upstream of cba a sequence comprising 294 nucleotides was identical to the sequence upstream of the structural gene of colicin E1, with the exception of 43 single-nucleotide replacements, additions, or deletions. Apparently, the region upstream of colicins B and E1 and the channel-forming sequences of colicins A and B have a common origin.
mesh_terms: D000595:Amino Acid Sequence; D003086:Bacteriocin Plasmids; D001483:Base Sequence; D003001:Cloning, Molecular; D003087:Colicins / Q000235:genetics*; D005798:Genes, Bacterial; D005809:Genes, Regulator; D007473:Ion Channels; D010957:Plasmids; D011487:Protein Conformation
chemical_list: D003087:Colicins; D007473:Ion Channels