The significance of the coat protein in infection by the electrophoretic forms of cowpea mosaic virus

Abstract

The specific infectivity of purified cowpea mosaic virus (CPMV) increased with increasing age of infection. However, the specific infectivity of the extracted CPMV-RNA declined with age of infection and this decline was correlated with increased polydispersity. Increased specific infectivity of CPMV particles was correlated with an increase in the ratio of the fast-migrating to slow-migrating electrophoretic form. The fast form (F) demonstrated a greater specific infectivity than the slow form (S), but F-RNA was less infectious than S-RNA and was more polydisperse. Exposure of the separated forms to basic proteins and ribonuclease reduced the specific infectivity of the F form more than the S form. In etiolated cowpea hypocotyls infection was initiated more rapidly with the F form than with the S form. These data suggest that the modified protein coat of the F particles is responsible for the enhancement of infectivity.