Synthesis of a brain-specific protein (S100 protein) in a homologous cell-free system programmed with cerebral polysomal messenger RNA.

Polyribosomes, carrying nascent polypeptide chains, were prepared from whole brain, cortex, and hindbrain-medullary white matter of young adult rats. In a homologous cell-free system, a brain-specific protein (S100 protein) was identified in the mixture of polypeptides released from the polyribosomes during incubation for 1 hr at 37 degrees . De novo synthesis of the S100 protein was achieved in a reconstituted cerebral cell-free system containing polysome-derived mRNA and 40S + 60S subunits. The radioactively labeled S100 protein synthesized in vitro was identified by precipitation with antibody to S100 after addition of purified S100 as a carrier, and migration of the solubilized precipitate on acrylamide gels in the presence of sodium dodecyl sulfate. In vitro synthesis of the S100 protein did not occur in analogous cell-free systems derived from hepatic tissue or in a heterologous system containing liver polyribosomes and cerebral enzymes.