Protein Synthesis in Cowpea Mosaic Virus-infected Cowpea Protoplasts: Further Characterization of Virus-related Protein Synthesis

Inoculation of cowpea protoplasts with purified middle component of cowpea mosaic virus (CPMV) did not result in the production of newly induced virus-related proteins. In contrast, infection of protoplasts with purified bottom component produced virus-related polypeptides with mol. wt. 170x10³, 112 x 10³, 110 x 10³, 84 x 10³ and 30 x 10³, but not the virus capsid proteins. These results suggest that CPMV B-RNA specifies one or more early functions, one of which is the replicase function, while M-RNA encodes the virus coat proteins. Attempts to elucidate the mechanism by which the virus-specific proteins are synthesized were inconclusive. No precursor-product relations could be demonstrated and virus subgenomic messengers were not observed. Some kind of processing was nonetheless found to occur with the small virus capsid protein:several discrete oligopeptides were successively cleaved from this protein after assembly into the virion particle.

^* Present address: Institute of Virology, Veterinary Faculty, State University, Yalelaan 1, Utrecht, The Netherlands.