Various plants contain enzymes called ribosome inactivating proteins (RIPs), officially called rRNA N-glycosidases, which inhibit protein synthesis by cleaving a single N-glycosidic bond of 28S rRNA. RIPs have been isolated from many different plants species such as Pokeweed (Phytolacca americana), P. acinosa and the four o'clock flower or marvel of Peru (Mirabilis jalapa). RIPs have shown broad spectrum antiviral activity against RNA, DNA of plant and animal viruses including tobacco and potato mosaic viruses, poliovirus, herpes simplex virus (HSV), cytomegalovirus, influenza virus, and human immunodeficiency virus (HIV)-1 . Three distinct antiviral proteins with similar activities have been identified in pokeweed. PAP-I, PAP-II, and PAP-S are the forms of pokeweed antiviral protein (PAP) that appear in spring leaves, summer leaves, and seeds, respectively. Exogenous application of small amounts of PAP to the surface of plant leaves completely prevents mechanical transmission of unrelated viruses to several different host plants.