Infectious process of the parvovirus H-1: correlation of protein content, particle density, and viral infectivity

The infectious particles of the parvovirus H-1 were characterized with respect to protein content, density in CsCl, and specific infectivity. Heavy-full and light-full particles were purified from infected simian virus 40-transformed newborn human kidney (NB) cells and from simian virus 40-transformed hamster kidney (THK) cells. Analysis of the protein content of these particles demonstrated that the ratio of viral protein VP2' to VP2 was the same in heavy-full and light-full particles derived from the same cell line, but differed significantly between the two hosts. However, the infectivity of the particles from each cell line was the same for all four viral species.. Also, in vitro conversion of VP2' to VP2 did not enhance the particle infectivity of either heavy-full or light-full virus. When the fate of input virus was studied with 125I-labeled H-1, the conversion of VP2' to VP2 occurred in a time-dependent manner up to 24 h postinfection. Simultaneous with the proteolytic cleavage, there was a shift in the density of the heavy-full virus to the light-full density. However, protein analysis of the 125I-labeled light-full virus at various times postinfection indicated that they were not enriched in VP2 when compared with heavy-full virus or the total virus population. Thus, the cleavage of VP2' to VP2 is not responsible for the shift in density from heavy-full to light-full virus, and although these events might be required for infection they appear not to be interdependent.