Amino acid sequence of immunity protein (B subunit) of colicin E3

The amino acid sequence of immunity protein (protein B) of colicin E3 (84 amino acid residues) was determined. B was first split into two fragments, CB 1 and CB 2, by CNBr treatment. The structure of CB 1 (the N-terminal part of B) was determined by Edman degradation of whole protein B. The structure of CB 2 (the C-terminal part of B) was established by sequencing its four trypsin peptides. The sequences and the alignment of the tryptic peptides were completed by analyses of thermolysin peptides of CB 2. These results established the complete amino acid sequence of B.