Detailed biophysical, biochemical, and structural studies rely on the preparation of milligram amounts of pure recombinant proteins. Many useful overexpression systems have been developed for this purpose (1 –3 ), and of these, bacterial overexpression is still the most convenient and simplest to use (4 –6 ). Because many proteins are only active as heteromeric complexes, there has been much recent interest in preparing such complexes using recombinant technology (7 –10 ). The preparation of complexes generally relies on the ability to reconstitute such protein complexes from individually prepared recombinant proteins (10 –13 ), a process that often involves refolding (14 ,15 ). This is generally not ideal, and in cases where one protein is unstable without the other (16 ), impossible.