(A) A working model for late nuclear steps of yeast 60S ribosomal subunit assembly. Entry and exit points for assembly factors in wild-type cells are indicated. In the L8Δ1-70 strain, remodeling events downstream from the association of Mtr4 are blocked, Rpf2 and Rrs1 cannot dissociate from pre-ribosomes, and Sda1, Rea1, and Ipi1-Rix1-Ipi3 cannot associate with assembling ribosomes. (B) The high-resolution cryo-EM structure of Nog2-associated particles shown from the subunit-interface (PDB accession number 3JCT). Domain V is colored dark blue while 5.8S rRNA and 5S rRNA are colored black and dark gray, respectively. (C) The pre- and post-rotated structures of the central protuberance (5S rRNA, L11, and L5) and assembly factor Rsa4 are modeled on the cryo-EM structure of Nog2-associated pre-ribosomes. In the post-rotated state of the central protuberance, assembly factors Rpf2 and Rrs1, which are present in the pre-rotated state, are no longer present and assembly factor Sda1 associates with pre-ribosomes. Note that the binding site of Sda1 overlaps with that of Rpf2.
