An open interface in the pre-80S ribosome coordinated by ribosome assembly factors Tsr1 and Dim1 enables temporal regulation of Fap7

Bridges formed and not formed in 80S-like ribosomes. (A) The bridges between 60S and 40S head and central region of the body are largely not formed (blue patches), while those with the pre-40S foot remain intact or modestly reorganized (pink). (B) In mature ribosomes, helix 69 from the 60S subunit (H69, cyan) binds helix 44 from the pre-40S subunit (h44, yellow, model from PDB ID 3J77 [Svidritskiy et al. 2014]). 80S-like ribosomes join through a novel bridge B2a/c where H69 (cyan) joins a repositioned h24 (yellow). (C) H69 and h24 fit into the density at the subunit interface near a bilobed density that corresponds to Dim1 (dark blue).