[Protein kinase activity of RNA-binding proteins from amphibian oocytes]

RNA-binding proteins isolated from amphibian oocytes ribosome-free extract by affinity chromatography on poly (U)-Sepharose possess an endogenous protein kinase activity. Incubation of these proteins with [gamma-32P] ATP leads to the incorporation of labelled phosphate into 6-7 polypeptide chains with molecular masses from 20 000 to 80 000, which are estimated by disk-electrophoresis in the presence of sodium dodecyl sulphate, followed by autoradiography of dried gels. High-voltage paper electrophoresis of acid hydrolysates of labelled proteins showed that mainly [32P]phosphoserine is formed in this reaction. Phosphorylation is not stimulated by cAMP and reaches its maximum by 20 degrees and pH near 8. The presence of poly(U) in the reactional mixture inhibits phosphorylation considerably. The opportunity of partial decrease or loss of RNA-binding activity due to phosphorylation of RNA-binding proteins is discussed.