2ZKR STRUCTURE OF A MAMMALIAN RIBOSOMAL 60S SUBUNIT WITHIN AN 80S COMPLEX OBTAINED BY DOCKING HOMOLOGY MODELS OF THE RNA AND PROTEINS INTO AN 8.7 A CRYO-EM MAP RIBOSOMAL PROTEIN/RNA, PROTEIN-RNA COMPLEX, 60S RIBOSOMAL SUBUNIT, RIBOSOMAL PROTEIN/RNA COMPLEX