Fine Structure of the Cytoplasmic-Polyhedrosis Virus of the Silkworm, Bombyx moril

Abstract

The fine structure of the cytoplasmic-polyhedrosis virus (CPV) of the silkworm was studied with special reference to the spherical particle (SP) attaching to the top of projections of the virions. The SPs were observed in both liberated and free CPV which were purified with a cushion of 50% sucrose from freshly prepared samples. These SPs were homogeneous in size and shape, and attached only to the top of projections but not to the other parts of the CPV. The size of SP was about 12nm in diameter. After treatment of CPV with fluorocarbon (50%), ether (50%), DOC (0.5%) or trypsin (0.5mg/ml), SPs could not be detached from the top of projections. Some copolymer-like structures of SP (or SP-like particle) were also observed. Their overall size were about 60-70nm, apparently smaller than that of CPV (about 100-110nm). They appeared to be a subunit structure as hexamer or higher co-polymer, consisting of SPs, projection-like structures and large spherical particles. Sometimes, such polymer existed on the top of projections of CPV. Nothing has been known about the nature and role of these polymer for the CPV infection in the silkworm.