Fig. 4. P49 functions upstream of P35 but downstream of Op-IAP. (A) P49 inhibits P35 cleavage. Sf21 cells were mock-infected (mi) or infected with viruses vP49 (+p49), vOp-IAP (+iap) or vΔp35 (–p35) with (lanes 2–5) or without (lanes 6–8) wild-type p35⁺ virus (+P35). Lysates (3 × 10⁵ cell equiv) prepared 24 h later were subjected to immunoblot analysis using α-P35. Top: P35 and its C-terminal cleavage product (*) are indicated. (B) Op-IAP inhibits P49 cleavage. Lysates (10⁶ cell equiv) prepared 24 h after infection with the viruses described in (A) with (lanes 2–5) or without (lanes 6–8) vP49 (+P49) were subjected to immunoblot analysis with α-P49. SF21 cells constitutively expressing Op-iap (IAP) were included (lane 9). (Top) P49 and its C-terminal cleavage fragment (*) are indicated. The P49-related protein (filled diamond) is marked.