The nucleocapsid of Berne virus.

Abstract

In Berne virus-infected cells and in gradient-purified virions two major proteins with mol. wt. of 20K and 22K were detected. The 22K species is thought to represent the main envelope polypeptide; in infectious culture media it was present in a low envelope polypeptide; in infectious culture media it was present in a low density substructure which could be quantitatively converted into slowly sedimenting material by detergent treatment. The 20K polypeptide (accounting for about 80% of the 14C-amino acid label in the virion) was phosphorylated, occurred in an intracellular substructure of higher density than the virion (rho = 1.36 g/ml in CsCl) and was the only viral protein possessing RNA-binding properties; it was recognized preferentially by heterologous animal sera in immune precipitation. The 20K species is therefore identified as the main capsid protein. Two additional polypeptides (19K and 17K) were regularly detected in extracts of infected cells; they appeared to share oligopeptides with the 20K protein and are interpreted as being proteolytic cleavage products. The nucleocapsid of Berne virus was visualized after ether treatment as a flexible bacilliform structure with conspicuous transverse striation. Demonstration of a 20K nucleocapsid protein further supports the authors' proposal that Berne virus is a representative of a new family of enveloped RNA viruses (Toroviridae).