Contact of Rsa4 to Nsa2, Rpl5 (uL18), and Rpl12 (uL11) on the pre-60S subunit. The crystal structures of Rsa4 (blue) and the Nsa2 peptide (residues 85–96; red) were fit into the 8.7-Å resolution cryo-EM structure of the Arx1 pre-60S particle. (A) Close view of the electron density of Rsa4 from the subunit joining (left) and solvent site (right). (B) Contact of Rsa4 to neighboring proteins Rpl5 (uL18, green) and Rpl12 (uL11, orange) viewed from the subunit joining site (left) and from the opposite site (right).