Transformation of E. coli BL21 with plasmids carrying the tag-less CFA/I/II/IV MEFA gene yielded recombinant strain 9472. Strain 9472 expressed tag-less CFA/I/II/IV MEFA protein as effectively as strain 9175 expressed 6xHis-tagged MEFA. Tag-less CFA/I/II/IV MEFA protein was extracted at an average yield of 150 mg per liter culture (an average of five purifications) after refolding. Coomassie blue staining showed the tag-less MEFA protein was extracted at an estimated purity of over 95% (Figure 1).