SDS-PAGE of 10–40% sucrose gradients of material produced by co-expression of (A) 80α gp47 + SaPI1 CpmB (strain ST112); (B) gp47 + SaPI1 CpmA and CpmB (ST114); (C) gp46+gp47+CpmA+CpmB (ST118). Lanes M, marker, MW (kDa) indicated; S2, high-speed supernatant; P2, high-speed pellet. The arrow indicates the direction of the gradient. Lane P is the gradient pellet fraction. Bands corresponding to the known positions of 47*, 46* and CpmB are indicated, where appropriate. The procapsid fraction is indicated by the big arrowhead in (C).