Influence of C-terminal modifications of phi X174 lysis gene E on its lysis-inducing properties

The phi X174 gene E product (gpE) causes lysis of Escherichia coli by inducing the host autolytic system. Experiments were carried out to ascertain which part of the 91 amino acid polypeptide carries the functional site for this process. For this purpose fusion genes were created comprising the first 51 codons of gene E and unrelated sequences coding for 102 or 33 amino acids respectively. The chimeric protein of 153 amino acids consisting of the N-terminal part of gpE and a fragment of beta-galactosidase, was neither able to lyse E. coli nor to restore beta-galactosidase activity by alpha-complementation. Expression of the 84 amino acid polypeptide, however, was able to induce lysis of E. coli. It is therefore concluded that the functional lysis-inducing site of gpE is located within the cloned N-terminal part of gene E. In the shorter chimeric protein the sequence following the functional site was tolerated or necessary for stabilization, but in the longer chimeric protein, the C-terminal sequence disturbed the lysis-inducing conformation.