Identification and Characterization of Ribosomal Proteins Phosphorylated in Vaccinia-Virus-Infected HeLa Cells

Two-dimensional analysis of 32P-labelled ribosomal proteins revealed three proteins which are phosphorylated in vaccinia-virus-infected HeLa cells. All three proteins belong to the 40-S ribosomal subunits and were identified as S2, S6 and S16. The ribosomal protein S6 is phosphorylated also in uninfected HeLa cells. Phosphoserine was detected in all three proteins, phosphothreonine only in the protein S2. Phosphorylation of these ribosomal proteins in infected cells is dependent on the multiplicity of the viral infection and increases during the first six hours of infection. All three proteins are also phosphorylated in virus-infected cells treated with cycloheximide and in cells infected with ultraviolet-irradiated virus. This suggests that the phosphorylation reaction involves a vaccinia virion-associated protein kinase.