Three-dimensional structure of the wild-type RHDV

The three-dimensional (3D) structure of the wild-type rabbit hemorrhagic di sease virus (RHDV) has been determined to a resolution of 3.2 nm by electro n cryomicroscopy and computer image reconstruction techniques. The 3D densi ty map exhibits characteristic structural features of a calicivirus: a T=3 icosahedral capsid with 90 arch-like capsomeres at the icosahedral and loca l 2-fold axes and 32 large surface hollows at the icosahedral 5- and 3-fold axes. This result confirms that the RHDV isolated in China is a member of the Caliciviridae family. A rather continuous capsid shell was found withou t channels. However, our RHDV structure also reveals some distinct structur al characteristics not observed in other caliciviruses, including interconn ected capsomeres and the lack of protuberance on the base of each of the su rface hollows. Two types of particles were identified with similar outer ca psid structure but different density distributions inside the capsid shells , which could not be distinguished by conventional negative staining electr on microscopy. As the genomic and subgenomic RNAs are both packaged into pa rticles for RHDV, we suggest that the two types of particles identified cor respond to those containing either the genomic or subgenomic RNAs, respecti vely.