Schematic structures of His-ILFAC and His-FAC. The structures are drawn approximately to scale. The restriction sites and sequence (BamHI site in italics) of the IL-3–FAC junction are indicated. The last two codons for IL-3 at the carboxy terminus, a two-residue linker, and the first two mature codons of FAC are also shown. Hexahistidine tag (filled block), mature gibbon IL-3 (striped block), FAC (open block).