53 - PROPERTIES OF A PARTIALLY PURIFIED FRACTION CONTAINING CYTOSOLIC PROTEIN(S) NECESSARY FOR YEAST MITOCHONDRIAL PROTEIN SYNTHESIS

Abstract

Protein synthesis in isolated yeast mitochondria can be stimulated 6-8 fold by addition of dialyzed postpolysomal supernatant at the start of the incubation. The protein factor(s) which stimulate protein synthesis have been partially purified by incubating the postpolysomal supernatants with 0.5M potassium phosphate prior to chromatography on Sephacryl G-200. Stimulatory activity was eluted equally in two peaks, one in the 40 to 80,000 molecular weight range and one with a molecular weight 10,000 or less. Stimulation of mitochondrial protein synthesis by the low molecular weight activator fraction was inhibited by chloramphenicol and proportional to the protein concentration of activator added. The rates obtained with 40 pg of activator were 20-fold greater than that achieved by mitochondria alone and represented a 45-fold purification of the activity present in the postpolysomal supernatant. The activator also stimulated the incorporation rate when GTP or GDP was present in the medium suggesting that low molecular weight protein(s) present in the cytosol are necessary for optimal rates of mitochondrial protein synthesis.