Nucleotide sequence of the structural gene for colicin E1 and predicted structure of the protein

We have determined the nucleotide sequence of the structural gene for colicin E1, which consists of 1,566 base pairs. The amino acid sequence (522 residues) of the protein was derived from the DNA sequence, and the molecular weight was calculated to be 57,279. From the analysis of the predicted secondary structure, there appear to be three consecutive long alpha-helices in the NH2-terminal half of the polypeptide, spanning 40, 100, and 35 amino acid residues. In addition, there is a polypeptide region near the COOH terminus that shows homology to the NH2-terminal signal portions of outer membrane lipoprotein in Escherichia coli and beta-lactamase in Bacillus licheniformis. Most of the homologous amino acids are located in the region where either alpha-helix or beta-sheet would be expected to occur, as determined from the amino acid sequence. These characteristics of the predicted protein structure might correspond to properties of colicin E1 as an ionophore in its antimicrobial action and also as an exported protein during its induced synthesis.