Modifications of ribosomes have been investigated in human epidermoid carcinoma-2 cells at different stages of herpes simplex virus type 1
infection. Very early in
infection, there is an increase in
ribosomal protein S6 phosphorylation even in the absence of serum. The same result is obtained in the presence of
actinomycin D. At early
infection time,
ribosomal proteins S2, S3a and Sa are newly phosphorylated. At early and early-late times, three phosphorylated non-
ribosomal proteins (v1, v2 and v3) are differently associated temporally to ribosomes. Analyses of
proteins extracted from 40S subunits, 80S ribosomes and polysomes show that v1 and v2 are distributed differently among the different ribosomal populations. S6
phosphopeptides were found to be identical after serum stimulation and after
viral infection. In every case
phosphoserine and
phosphothreonine were identified in S6. Only
phosphoserine was found in other phosphorylated
proteins. Our results indicate that herpes simplex virus type 1 is able to modify pre-existing ribosomes: (i) by stimulating a pre-existing
kinase for S6 phosphorylation even in the absence of serum and of viral genome expression; (ii) by inducing new specific
kinase activity(ies); and (iii) by association of new, phosphorylated
proteins to ribosomes. These ribosomal modifications are correlated with changes in
protein synthesis, as shown by two-dimensional electrophoretic analyses of newly synthesized 35S-labelled
proteins.