Hepatitis A virus subviral particles: purification, accumulation, and relative infectivity of virions, provirions and procapsids

Summary

Virus-specific particles were isolated from hepatitis A virus (HAV)-infected cells and the role of each particle type in the replicative cycle assessed. Mature virions, provirions (immature virions) and empty capsids (procapsids) were detected in cell lysates, and both virions and provirions were found in the culture supernatant. Particle types were separated by isopycnic caesium chloride gradient- or linear sucrose density gradient-ultracentrifugation, and their capsid proteins characterised. Virions, provirions and procapsids containing both VP1 and varying levels of the VP1 precursor protein PX were found, suggesting that trimming of PX is not essential for particle formation. Provirions (containing VP0) and virions (containing VP2) could not be clearly separated with these techniques, but sucrose gradients allowed greater separation of particle pools with distinct VP0 contents and specific infectivities which could be used for further studies of the biological role of VP0 cleavage. Virions, with a higher sedimentation coefficient and buoyant density presumably reflecting a more compact structure, had a higher relative infectivity when compared to provirions. HAV-infected cells therefore contain a heterogenous mixture of RNA-containing viral particles with characteristics between those of true provirions and virions, but all such particles are released from the cell and can participate in further rounds of infection.