Partial purification of cytosolic proteins which control yeast mitochondrial protein synthesis.

Abstract

Protein synthesis in isolated yeast mitochondria incubated in the presence of GTP is stimulated 2-fold by addition of dialyzed postpolysomal supernatant (S-150) at the start of the incubation. Incubation of the yeast S-150 with 5'-nucleotidase had no effect on the stimulatory activity suggesting that the increased protein synthesis does not result from guanine nucleotides. A partial purification of the protein factors which stimulate mitochondrial protein synthesis has been accomplished by chromatography on Sephacryl S-200. Stimulatory activity was eluted in two peaks, one in the 40,000 to 80,000 molecular weight range and a broad peak with a molecular weight of less than 10,000. Stimulation of mitochondrial protein synthesis by the low molecular weight activator fraction was proportional to the concentration of protein added and abolished by trypsin treatment suggesting that the low molecular weight activator is a protein(s). The rate of mitochondrial protein synthesis in the presence of activator, was linear for 40 min, while that in the presence of GTP was linear for only 20 min, suggesting that the activator and GTP stimulate protein synthesis by different mechanisms. Analysis of the products of the stimulated mitochondrial protein synthesis by gel electrophoresis revealed that the activator increased equally the labeling of all products. These results indicate that low molecular weight proteins present in the cytosol regulate mitochondrial protein synthesis.