A DNA segment within the colicin E1 structural gene on ColE1 affecting immunity to colicin.

Insertion of DNA at the EcoRI site of ColE1 results in increase of immunity to colicin killing in E. coli harboring such recombinant ColE1 plasmid as compared to E. coli (ColE1). This effect is neither due to cis or trans interactions originating from the inserted foreign DNA fragment, nor to changes in plasmid copy number. This defect in the immunity mechanism is not trans complemented for by wild type ColE1. Increase in immunity can also be obtained by deleting a DNA segment from the ColE1 genome. This segment is approximately 120 bp left to the EcoRI site within the colicin structural gene. It is concluded that the structure of DNA per se, around the EcoRI site, within colcin structural gene, is the structure which affects immunity expression.