Expression and purification of His-FAC and His-ILFAC. (A) Lysates from uninduced (lanes 1 and 4) or induced (lanes 2 and 5) E coli or solubilized proteins (lanes 3 and 6) that were immobilized on Ni²⁺-agarose, eluted with acid buffer, and analyzed by 10% SDS-PAGE and Coomassie blue staining. (B) Purification of His-ILFAC by size exclusion chromatography. Soluble His-ILFAC obtained after Ni²⁺-agarose chromatography was resolved further over Superdex-75. Fraction 1, wash buffer; fractions 2 and 3, void volume containing protein peaks as assessed by chromatography tracing (data not shown); fraction 4, void volume containing no protein as predicted by the flat chromatography tracing (data not shown). A 50-kD protein copurifying with His-ILFAC, His-IL▵FAC, most likely results from premature termination of translation as it is immuoreactive with an anti-His antibody. However, carboxy-terminal degradation cannot be excluded.