Translational inhibition in extracts from serum-deprived animal cells

When Vero M3 cells, a line of African green monkey kidney cells, are deprived of serum during exponential growth they display a decreased net rate of intracellular protein synthesis. Cytoplasmic extracts prepared from these serum-starved cells have a diminished capacity to promote protein synthesis mediated by endogenous mRNA when compared to their non-deprived counterparts. This diminished translational capacity is not due to a limitation in mRNA since the amount of polyribosomes remains constant during the time of serum starvation used in this work. These same extracts also have a reduced capacity to promote polyphenylalanine synthesis mediated by exogenously added polyuridylate. By supplementing extracts with a post-ribosomal supernatant fraction from HeLa cells polyphenylalanine synthesis mediated by polyuridylate can be stimulated ten-fold for extracts prepared from serum-deprived cells, but only two-fold for control extracts. These observations can be explained by postulating that serum deprivation alters the protein synthetic machinery of the cell by producing either an inhibitor or deficiency in some component required for translation of mRNAs.