Experimental electron density of E site ligands bound to the H. marismortui 50S ribosomal subunit. (A) Fo(complex)–Fo(parent) electron density map of CCA bound to the 50S subunit, calculated with experimental phases, contoured at 4 σ. Electron density is visible for the portion of ribosomal protein L44e that adopts an altered conformation upon tRNA binding, near the top of the frame. (B) Fo(complex)–Fo(parent) electron density map of the minihelix bound to the 50S subunit, using experimental phases, contoured at 3 σ. Electron density gets weaker further from the CCA end because of increasing disorder. Density for the mobile portion of L44e is at the bottom of the frame.
