Colicin E2 is encoded by the SOS-inducible colicin operon of plasmid ColE2-P9. Highly induced colicin E2 is excreted from the E. coli host cell, accompanied by quasi-lysis and cell death. These three events are all directed by the colicin lysis protein that comprises the signal peptide and a small mature lipoprotein. We constructed a mutant lysis gene encoding its complete signal peptide with addition of two external amino acids at the C-terminus. By using this mutant peptide as a reference, the wild type lysis signal peptide was identified and shown to remain quite stable after the cleavage. This mutant peptide also mimics the cleaved-off signal peptide avoiding the influence of the mature lysis lipoprotein, and suggested that cell death by the lysis protein, but neither colicin excretion nor quasi-lysis, is decided by the nature of its signal region.