Purification and properties of the components of cowpea mosaic virus.

Abstract

Abstract Purified preparations of cowpea mosaic virus (CPMV) consist of three centrifugal components with sedimentation coefficients of 58, 95, and 115 S, referred to as respectively top, middle, and bottom component. Purification of CPMV by the butanolchloroform method resulted in a considerable loss of virus and partial destruction of the top component. Precipitation of virus by 4% polyethylene glycol and 0.2 M sodium chloride was a fast procedure, gave high yields of purified virus, and gave preparations with the same relative amounts of the three components as occurred in crude plant sap. The rate of increase of the individual components in the plant was independent of the amount of the other components present. It appears that the components are synthesized concurrently and do not arise by conversion of one component into another. The three components were separated by sucrose gradient centrifugation. The bottom component alone was infectious, but not the middle or top component. Addition of the middle component to bottom component had no substantial effect on the infectivity. The top component did not contain nucleic acid whereas the amount of RNA in the middle component was estimated to be 23% and in the bottom component 32%. RNA isolated from purified middle component had one sharp peak in the analytical ultracentrifuge with a sedimentation coefficient of 22 S. Bottom component also contained only RNA of one size with a sedimentation coefficient of 28 S. Bottom component RNA had equimolar amounts of adenylic acid and uridylic acid which together accounted for 58% of the nucleotides. The base composition of middle component RNA differed from that of bottom component as it appeared to be richer in uridylic acid and poorer in guanylic acid. The possible relationship of the components is discussed.