Expression of the ColE3 operon in maxicells.

The cea, cei, and cel genes of the ColE3 operon were localized and characterized by subcloning and by transposon mutagenesis. Plasmids containing different portions of the ColE3 operon were transformed into an E. coli maxicell strain CSR603. Proteins encoded by these plasmids were analyzed by SDS-PAGE after UV irradiation of the cells. The results showed that the molecular weights of Col, ImmE8, ImmE3 and Lys were 60 kDa, 15 kDa, 10 kDa, and 4-5 kDa, respectively. These results indicated that the maxicell system provides an easy and simple method for the identification of plasmid-encoded proteins.