A POSSIBLE MECHANISM FOR THE ANTIVIRAL ACTIVITY OF POKEWEED ANTIVIRAL PROTEIN

The mechanism by which pokeweed antiviral protein (PAP) inhibits the infection of tobacco by TMV was investigated. The N-glycosidase activity of PAP was measured using a combination of aniline treatment to cleave the rRNA at the depurinated site, gel electrophoresis and Northern blot hybridization using a probe specific for the 3′ end of tobacco 25S rRNA. Using this assay it was found that the host ribosomes, which are used by viruses to uncoat and to synthesize replicases at an early stage of infection, were depurinated and probably inactivated by PAP as early as 5 min after inoculation. It was also found that the extent of the inhibition of virus infection and the depurination of host ribosomes were positively correlated with the concentration of PAP. These results suggest that the depurination and inactivation of host ribosomes is the cause of the inhibition of virus infection by PAP. © 1993 Academic Press, Inc.