Association of mRNA with 40S subunits and 80S ribosomes before and after treatment with eIF5, ΔeIF5B, and 60S subunits of 48S complexes assembled on 20nt-AUG-17nt (A), 20nt-AUG-32nt (B), 35nt-AUG-32nt (C), 35nt-AUG-17nt (D), and (U5)-30nt-AUG-28nt (E) mRNAs, as indicated. Association of 32P-mRNA with ribosomal complexes was assayed by Cerenkov counting after sucrose density gradient centrifugation. (F) 80S complex formation after treatment with eIF5, ΔeIF5B, and 60S subunits (as indicated) of 48S complexes assembled on 20nt-AUG-17nt mRNA. Ribosomal complexes were separated by sucrose density gradient centrifugation and assayed by measuring optical density. Ribosomal complexes are indicated above appropriate peaks. Upper fractions from gradients have been omitted for clarity. (G) UV cross-linking of 32P-(U5)-30nt-AUG-28nt mRNA to components of sucrose density gradient-purified 48S complexes before and after induction of hydrolysis of eIF2-bound GTP and in binary complexes with eIF3j- and eIF3j+. UV cross-linked eIF3 subunits and ribosomal proteins are indicated.