Extracts from encephalomyocarditis (EMS) virus infected Krebs II ascites carcinoma cells pulse-labeled during the active virus-specific synthesis and then chased were fractionated in a sucrose concentration gradient. It has shown that some radioactivity was detectable in the polysome region as well as in the regions of ribosome monomers and ribosomal subunits. An analysis of the radioactive material in a CsCl density gradient and by polyacrylamide gel electrophoresis has shown that components of the protein-synthesizing system in infected cells are bound to some proteins, the electrophoretic mobility of which corresponds to that of polypeptides found in the infected cells, namely, polypeptides G 16 (18 kdalton) and 22 (22 kdalton). The ribosomes from normal cells were also found to be associated with three labeled polypeptides, their molecular weight (89-90, 43-48 and 39-40 kdalton) being different from those of the polypeptides bound to the ribosomes from the infected cells. Thus, the presence of polypeptides G and 22 is specific for ribosomes isolated from the infected cells. The possible significance of this binding is discussed.