Visualization of ordered genomic RNA and localization of transcriptional complexes in rotavirus.

In double-stranded-RNA (dsRNA) viruses found in animals, bacteria and yeast, the genome is transcribed within the structurally intact core of the virion with extraordinary efficiency. The structural organization of the genome and the enzymes involved in the transcription inside any of these viruses, critical for understanding this process, is not known. Here we report what we believe is the first three-dimensional characterization of the viral genome and the transcription complex in a prototypical dsRNA virus. Rotavirus is a large (diameter 1,000 A) icosahedral virus composed of three capsid protein layers and 11 dsRNA segments. It is the most important cause of gastroenteritis in children, accounting for over a million deaths annually. We show that viral dsRNA forms a dodecahedral structure in which the RNA double helices, interacting closely with the inner capsid layer, are packed around the enzyme complex located at the icosahedral 5-fold axes. The ordered RNA accounts for about 4,500 out of a total 18,525 base pairs in the genome, the largest amount of icosahedrally ordered RNA observed in any virus structure to date. We propose that the observed organization of the dsRNA is conducive for an orchestrated movement of the RNA relative to the enzyme complex during transcription.