Ribosomal subunits from Tetrahymena pyriformis. Isolation and properties of active 40-S and 60-S subunits.

Tetrahymena pyriformis ribosomal subunits were obtained by incubation of post-mitochondrial supernatant in the presence of 0.2 mM GTP and 0.1 mM puromycin for 45 min at 28 degrees C, followed by sucrose density gradient centrifugation. Isolated 40-S subunits were able to reassociate in vitro in the presence of 5 mM MgCl2 and 50 mM KCl and to perform poly(U)-dependent protein synthesis. The 60-S subunit carries the peptidyl transferase activity. The number of proteins in T. pyriformis ribosomal subunits was determined by two-dimensional polyacrylamide gel electrophoresis. The 40-S subunit contains 30 different protein species (including two acidic proteins). The 60-S subunit contains 35 different protein species (including two acidic proteins). The proteins were numbered following the system of Kaltschmidt and Wittmann.