Abstract
A small but distinct amount of yeast acidic ribosomal proteins Al/A2 was detected in cytosol by immunoblotting on a two-dimensional gel electrophoretogram, while 38 kDa acidic protein A0 was not detected. The free forms of Al/A2 in the cytosol were eluted in gel filtration at the molecular mass of about 30 kDa under non-denaturation conditions, suggesting that they exist as a dimer or timer without association with A0. The amount of free Al/A2 was determined by immunoblotting to be 0.3% of the ribosome-bound Al/A2 in yeast. The time course of incorporation of radioactive amino acid showed that the cytosolic free Al/A2 are labeled more rapidly with high specific radioactivity than the ribosome-bound Al/A2. This result suggested that some of the cytosolic Al/A2, if not all, are newly-synthesized proteins which are ready for incorporation into cytoplasmic ribosomes.
