Does a cdc2 kinase-like recognition motif on the core protein of hepadnaviruses regulate assembly and disintegration of capsids?

Hepadnaviruses are enveloped viruses, each with a DNA genome packaged in an icosahedral nucleocapsid, which is the site of viral DNA synthesis. In the presence of envelope proteins, DNA containing nucleocapsids are assembled into virions and secreted, but in the absence of these proteins, nucleocaps ids deliver viral DNA into the cell nucleus. Presumably, this step is ident ical to the delivery of viral DNA during the initiation of an infection. Un fortunately, the mechanisms triggering the disintegration of subviral core particles and delivery of viral DNA into the nucleus are not yet understood , We now report the identification of a sequence motif resembling a serine- or threonine-proline kinase recognition site in the core protein at a loca tion that is required for the assembly of core polypeptides into capsids. U sing duck hepatitis B virus, we demonstrated that mutations at this sequenc e motif can have profound consequences for RNA packaging, DNA replication, and core protein stability. Furthermore, we found a mutant with a condition al phenotype that depended on the cell type used for virus replication. Our results support the hypothesis predicting that this motif plays a role in assembly and disassembly of viral capsids.