Z. Hong Zhou
from: Segmented Double-stranded RNA Viruses: Structure and Molecular Biology (Edited by: John T. Patton). Caister Academic Press, U.K. (2008)
The cytoplasmic polyhedrosis viruses (CPVs) form the genus Cypovirus of the family Reoviridae. CPVs are classified into 14 species based on the electrophoretic migration profiles of their genome segments. Cypovirus is unique among the Reoviridae in that it has only a single capsid shell, which is architecturally similar to the orthoreovirus inner core. Despite lacking protective outer shells, CPV exhibits striking capsid stability and is fully capable of endogenous RNA transcription and processing. The overall folds of CPV proteins are strikingly similar to those of their structural homologs in other reoviruses. However, CPV proteins have insertional domains and unique structures that contribute to their extensive intermolecular interactions. These differences, together with its unparalleled multiple modes of intermolecular complementarity, form the structural basis of the enhanced stability of CPV capsid. The CPV turret protein contains two methylase domains with a highly conserved helix-pair/β-sheet/helix-pair sandwich fold but lacks the β-barrel flap present in orthoreovirus λ2. The stacking of turret protein functional domains and the presence of constrictions and A spikes along the mRNA release pathway point to a mechanism that uses pores and channels to regulate the highly coordinated steps of RNA transcription, processing, and release read more ...