In addition to an irreversible stimulation of S6 ribosomal protein phosphorylation, there is a modification of a subset of ribosomal proteins by phosphorylation after herpes simplex virus type 1 (HSV-1) infection. Moreover, in the course of this infection, three additional phosphorylated proteins can be extracted from ribosomes and separated by two-dimensional electrophoresis (2-DE) of total ribosomal proteins. One of them exhibits an identical molecular mass to L30, while being more acidic. This protein is phosphorylated on serine residues. The kinetics of appearance of this protein in the ribosomal fraction correlated with a decrease in L30 staining, as shown by 2-DE. Determination of the N-terminal amino acid sequence of this extra phosphoprotein and of L30-derived peptides demonstrated the identity of these two proteins.