Conversion of the electrophoretic forms of cowpea mosaic virus in vivo and in vitro

Abstract

The electrophoretic forms of purified cowpea mosaic virus (CPMV) and bean pod mottle virus (BPMV) were examined by disc electrophoresis. The slow-migrating form (S) of CPMV predominated in early infection, and the fast-migrating form (F) predominated in late infection. The reverse relationship was true for BPMV. The transition from S to F in CPMV and F to S in BPMV suggested a precursor-product relationship between the electrophoretic forms. Evidence for this relationship was provided by kinetic studies of 32P incorporation into the forms of CPMV and by short-interval sequential yield data. When separated by density gradient electrophoresis, the F form of both viruses demonstrated a greater specific infectivity than the S form. The S to F conversion of CPMV was simulated in vitro by reaction with a mixture of carboxypeptidases A and B or chymotrypsin. This conversion of the electrophoretic forms of CPMV resulted in an increase in specific infectivity. The F to S conversion of BPMV was observed only after exposure to trypsin.