INHIBITION OF COWPEA MOSAIC-VIRUS REPLICATION BY ACTINOMYCIN-D

The effect of actinomycin D on the multiplication of cowpea mosaic virus (CPMV) in cowpea mesophyll protoplasts was studied. Using 10 μg/ml, a concentration at which actinomycin D reduced total RNA synthesis by more than 90%, propagation of CPMV was inhibited completely, provided the drug was present from the time of inoculation. The degree of inhibition of CPMV multiplication by actinomycin D progressively decreased with time after inoculation. At 8 hr after inoculation, a stage at which the infection is still in its latent phase, multiplication had become resistant to the antibiotic. Even under conditions of complete inhibition of virus replication, synthesis of virus antigen still continued as measured by staining of infected protoplasts with fluorescent antibodies made against purified virus. It was demonstrated that under these circumstances de novo production of viral top component (empty capsids) continued. Furthermore six virus-specific polypeptides were detected in CPMV-infected protoplasts. Their molecular weights were estimated to be 170,000; 110,000; 84,000; 37,000; 22,000; and 21,000. Of these the 37,000- and 22,000-molecular weight proteins probably represent the viral capsid proteins. Since all proteins were synthesized upon inhibition of host RNA synthesis by actinomycin D, it is concluded that they are specified by the viral genome. © 1979.