DNA ENCAPSIDATION BY VIRUS-LIKE PARTICLES ASSEMBLED IN INSECT CELLS FROM THE MAJOR CAPSID PROTEIN VP1 OF B-LYMPHOTROPIC PAPOVAVIRUS

Capsids of polyomaviruses-small, nonenveloped DNA viruses-consist of t he major structural protein VP1 and the minor structural proteins VP2 and VP3, The contributions of the individual capsid proteins to functi ons of the viral particle, such as DNA encapsidation, cell receptor at tachment, entry, and uncoating, are still not clear, Here we show that viruslike particles assembled in nuclei of insect cells from VP1 of t he monkey B-lymphotropic papovavirus (LPV) are sufficient to unspecifi cally encapsidate DNA. LPV VP1 expressed in large amounts in insect ce lls by a baculovirus vector assembled spontaneously in the nuclei to f orm viruslike particles, After metrizamide equilibrium density gradien t purification and nuclease digestion, a fraction of these particles w as shown to contain VP1-associated linear, double-stranded DNA with a predominant size of 4.5 kb, The fraction of DNA-containing VP1 particl es increased with time and dose of baculovirus vector infection, The D NA-containing particles, further purified by sucrose gradient centrifu gation, appeared as ''full'' particles in negative-staining electron m icroscopy, As shown by DNA hybridization, the encapsidated DNA consist ed of insect cell and baculoviral sequences with no apparent strong ho mology to LPV sequences, Three non-LPV VP1-derived host proteins with apparent molecular masses of approximately 14, 15, and 16 kDa copurifi ed with the DNA-containing particles and may represent insect cell his tones encapsidated together with the DNA, A similar species of host DN A was also found in purified LPV wild-type virions, These data suggest that LPV VP1 alone can be sufficient to encapsidate linear DNA in a s equence-independent manner.