Characterisation of protein synthesis in cell-free extracts from different mammalian cells by their sensitivity to inhibitors of polypeptide-chain initiation.

Plasma cells and reticulocytes are differentiated mammalian cell systems specialized in the synthesis of distinct proteins. To study whether a cell specificity of polypeptide-chain initiation in such cell systems can be detected through inhibitors, the sensitivity to several drugs interfering with initiation was compared in cell-free systems with S-30 extracts from these cells. The following was indicated by the experiments: (1) under the selected conditions, the different cell-free systems are comparable with respect to their activity of initiation, and that aurintricarboxylic acid inhibits mRNA binding to the ribosome in plasma cell tumours the same as in reticulocytes. (2) The sensitivity of translation of endogenous mRNAs in reticulocytes and plasma cell tumours to inhibitors of mRNA binding to the ribosome, aurintricarboxylic acid and the homopolynucleotides poly(U) and poly(A), are different. (3) Inhibition of the succeeding reactions of peptide-chain initiation by sodium fluoride and pactamycin was not selective. (4) In both cell systems translation of poly(U) is equally sensitive to aurintricarboxylic acid. (5) In extracts from TEPC 15 myeloma cells synthesis of immunoglobulin L-chains compared with that of the other myeloma proteins is partially resistant to aurintricarboxylic acid, whereas in reticulocytes, no differential sensitivities of individual proteins could be observed. The different susceptibility of the mRNA binding reaction in plasma cell tumours and reticulocytes suggests that the predominant mRNAs of these cells have different affinities to ribosome binding sites.