Protein yields obtained in the different expression hosts.

For each protein, the yield obtained is expressed in mg of target protein/liter of cell culture (black squares) and as percentage of total membrane protein (% TMP) (figures in brackets). –: protein not detected by western blot, ♦ = protein produced at a yield below 0.1 mg/L culture, ♦♦ = 0.1–0.5 mg/L, ♦♦♦ = 0.5–1 mg/L, ♦♦♦♦ = 1–4 mg/L, ♦♦♦♦♦ = 4–7 mg/L and ♦♦♦♦♦♦ >7 mg/L. n.a. = not applicable, as the two plant systems are not cultured in liquid media. n.c. = not cloned.