RAPID SENSITIVE ASSAY FOR SPECIFIC PROTEIN-SYNTHESIS IN CELLS AND IN CELL-FREE TRANSLATIONS - USE OF STAPHYLOCOCCUS-AUREUS AS AN ADSORBENT FOR IMMUNE-COMPLEXES

Formalin-fixed, heat-inactivated Staphylococcus aureus Cowen Type I (SAC) (Kessler, S. W. (1975) J. Immunol.115, 1617-1624) has been used to isolate antibody-bound tyrosine aminotransferase (EC 2.6.1.5) from radioactively labeled cell-free extracts and translation reactions of polysomes and poly(A)-containing messenger RNA. Under our conditions, SAC immunoprecipitation of cell-free extracts generated a radioactive background in control serum precipitations of 0.1%, an average of fivefold lower than backgrounds obtained by direct and indirect antibody precipitations. It is shown that the major source of the background, which limits sensitivity of the assay, comes from the amounts of antiserum and bacterial adsorbent in the assay. Procedures are presented to provide low backgrounds in more general applications of the precipitation method. From these experiments, SAC immunoprecipitation is shown to be a rapid, economical method to assay for specific protein synthesis under a variety of experimental conditions with noise levels much lower than with other standard methods. © 1979.