An in vivo and in vitro phosphorylation of yeast ribosomal proteins.

Phosphorylation of yeast ribosomal proteins has been demonstrated in vivo and in vitro. 32-P-labelled product represents an ester-linked class of phosphoprotein. Acrylamide-gel electrophoresis has shown that in both types of experiments radioactive proteins migrate similarly; this might indicate that closely related groups of proteins become phosphorylated in vivo and in vitro. In the presence of [32-P] ATP the amount of covalently bound phosphate was 1.0 - 1.2 moles/mole of ribosome. The phosphorylation of ribosomal proteins did not appreciably affect the activity of ribosomes in a cell-free protein-synthesizing system containing poly(U) and elongation factors.