Protein kinase associated with ribosomes of streptomycetes

Protein kinases can be classified into two main superfamilies on the basis of their sequence similarity and substrate specificity. The protein His kin ase superfamily which autophosphorylate a His residue, and superfamily Ser/ Thr and Tyr protein kinases, which phosphorylate Ser, Thr or Tyr residues. During the last years genes encoding Ser/Thr protein kinases have been iden tified in several microorganisms. Phosphorylation of proteins on Ser/Thr re sidues can be involved in many functions of prokaryotic cells including cel l differentiation, signal transduction and protein biosynthesis. Phosphoryl ation of prokaryotic protein-synthesizing systems showed that the phosphory lation of initiation and elongation factors is subject to alteration during cell differentiation or bacteriophage infection. Protein kinase associated with ribosomes of streptomycetes phosphorylate the elongation factor Tu an d 11 ribosomal proteins even in bacteriophage-uninfected cells. After phosp horylation of ribosomal proteins, ribosomes lose about 30 % of their activi ty at the translation of poly(U).