| Abstract: | Protein kinase previously detected in RNA-binding proteins of amphibian oocytes phosphorylates casein far more efficiently than histones to form phosphoserine and phosphothreonine and utilizes both ATP and GTP. Heparin in concentrations below 1 microgram/ml inhibits protein kinase. This allows to relate the enzyme to casein kinases II. Protein kinase was extensively purified (more than 15000-fold) with respect to proteins of ribosome-free extract. The homogeneous enzyme consists of three polypeptide chains (Mr 43,000, 41,000, and 29,000). The 125I-labelled enzyme possessing casein kinase and RNA-binding activities when injected into amphibian oocytes was detected in the particles identical to free cytoplasmic informosomes in terms of their sedimentation properties. |
