Cell-free protein synthesis: effects of age and state of ribosomal aggregation.

In cell-free extracts derived from Streptococcus faecalis, protein synthesis directed by endogenous messenger RNA increases as the culture ages. The increased activity is accompanied by an increase in the percentage of membranebound ribosomes and by a decrease in ribosomal monomers and subunits. These changes progress against a background of structural and compositional modifications in the membrane. Membrane modifications possibly related to endogenously directed protein synthesis in cell-free extracts include: (i) decreased specific activity of a membrane-associated polynucleotide phosphorylase capable of polysome degradation, and (ii) increased concentrations of certain phospholipids.