Persistence of ribosomal protein synthesis after infection of HeLa cells by herpes simplex virus type 1

D Simonin, JJ Diaz, T Masse and JJ Madjar Immuno-Virologie Moleculaire et Cellulaire CNRS UMR5537, Faculte de Medecine Lyon-RTH Laennec, France. Because synthesis of rRNA persists late during herpes simplex type 1 infection and because S6 phosphorylation is always correlated with efficient translation of ribosomal protein mRNA, we tested the hypothesis that ribosomal protein synthesis and ribosome biogenesis could persist after infection. At different times after infection, proteins were labelled with 35S for 1 h before harvesting and ribosomes were purified. Measurement of radioactivity incorporated into individual ribosomal proteins separated by two-dimensional PAGE demonstrated that ribosomal proteins are still synthesized and assembled into mature ribosomes up to late times during infection, while synthesis of beta-actin is severely inhibited. During expression of late genes, ribosome biogenesis was estimated to be 58% of that of the control as judged by [3H]uridine incorporation into rRNA. As for beta-actin mRNA, the level of ribosomal protein mRNA decreased progressively from the beginning of infection, reaching about 30% of the control level during expression of late genes. Taken together, these results demonstrate that ribosomal proteins are still synthesized up to the late time of infection and efficiently assembled into mature ribosomes, while there is a severe shutoff of the synthesis of other cellular proteins.