The Highly Ordered Double-Stranded RNA Genome of Bluetongue Virus Revealed by Crystallography

The concentration of double-stranded RNA within the bluetongue virus core renders the genome segments liquid crystalline. Powder diffraction rings confirm this local ordering with a 30 A separation between strands. Determination of the structure of the bluetongue virus core serotype 10 and comparison with that of serotype 1 reveals most of the genomic double-stranded RNA, packaged as well-ordered layers surrounding putative transcription complexes at the apices of the particle. The outer layer of RNA is sufficiently well ordered by interaction with the capsid that a model can be built and extended to the less-ordered inner layers, providing a structural framework for understanding the mechanism of this complex transcriptional machine. We show that the genome segments maintain local order during transcription.