Effect of ribosome-inactivating proteins on virus-infected cells. Inhibition of virus multiplication and of protein synthesis.

HEp-2 cells were infected with herpes simplex virus-1 (HSV-1) or with polio-virus I in the presence of plant proteins which inactivate ribosomes in cell-free systems, while exerting scarce effect on whole cells. Ribosome-inactivating proteins used were gelonin, from seeds of Gelonium multiflorum, an inhibitor from the seeds of Momordica charantia, dianthin 32, from the leaves of Dianthus caryophyllus (carnation), and PAP-S, from the seeds of Phytolacca americana (pokeweed). All proteins tested had the following effects: 1. They reduced viral yield; 2. They decreased HSV-1 plaque-forming efficiency; 3. They inhibited protein synthesis more in infected than in uninfected cells. These results strongly suggest that ribosome-inactivating proteins impair viral replication by inhibiting protein synthesis in virus-infected cells, in which presumably they enter more easily than in uninfected cells.