Peptidyl transferase center of rat-liver ribosome cores

Protein-deficient particles have been obtained by treating rat liver 80-S ribosomes or their 60-S subunits with 1 M NH4Cl in the presence of 50% ethanol at 0 degrees C (Po-cores) and 37 degrees C (P37-cores). The Po-cores from 80-S ribosomes are totally inactive in polyphenylalanine synthesis but fully active in the 'fragment assay' to test peptidyl transferase activity. The polymerizing activity of the cores is restored up to 40--50% of control activity by incubation in the presence of the split proteins. Three proteins are totally lost in the treatment, namely proteins L12, L40/41 ans S25. A series of up to nine different spots in the region of the L40/41 proteins are detected when the split fraction is analyzed by two-dimensional electrophoresis. This series of spots is, however, reduced to only two proteins when the second dimension is carried out in the presence of sodium dodecylsulphate. 80-S ribosome-derived P37-cores are about 80% active in the 'fragment reaction' while 60-S-subunit-derived particles are inactive in this assay. The inhibitory effect of a number of antibiotics is differentially affected by the treatment suggesting different localization of their binding sites. A comparative study of the proteins released by treatment in the two types of particles suggests the involvement in the peptidyl transferase center of the ribosome of one or more of the floolwing proteins: L21, L24, L27, L28 and L36.