DIFFERENTIAL PHOSPHORYLATION OF RIBOSOMAL ACIDIC PROTEINS FROM YEAST-CELL BY 2 ENDOGENOUS PROTEIN-KINASES - CASEIN-KINASE-2 AND 60S-KINASE

The native 80S ribosomes isolated from Saccharomyces cerevisiae (strai n W303) cells was phosphorylated by two endogenous protein kinases: mu ltifunctional casein kinase-2 (CK-2) and specific 60S kinase. Three ac idic proteins within the 60S ribosomal subunit: YP1 beta, YP1 beta' an d YP2 alpha are phosphorylated by both kinases. The other two proteins : YP1 alpha and YP2 beta are predominantly phosphorylated by CK-2 but not by 60S kinase. This was confirmed in the experiment with the recom binant protein, YP2 beta, as a substrate, which is practically not pho sphorylated by specific 60S kinase. These results together with the pr evious data based on the target amino-acid sequences suggest that, in addition to the multifunctional casein kinase-2 and specific 60S kinas e, there exist probably other protein kinase(s) which phosphorylate th e ribosomal acidic proteins in the cell.