Characterization of the tubules associated with the replication of three different orbiviruses

Abstract During the replication of bluetongue virus (BTV), African horsesickness virus (AHSV), and epizootic hemorrhagic disease virus (EHDV), tubular structures are synthesized in the infected cells. These tubules were purified on sucrose gradients and characterized. BTV and EHDV tubules are large with diameters of 68, and 54 nm, respectively. They have a surface fine structure with a striking 9-nm linear periodicity along the length of the tubules, giving them a ladder-like appearance. AHSV tubules are 18 run wide and have no clearly defined surface structure. The virus tubules are of indeterminate length, contain no RNA, and appear to be empty. They are in each case composed of a virus-specified noncapsid polypeptide of about 54,000 daltons. The AHSV tubule polypeptide is slightly larger than those of BTV and EHDV. Synthesis of the BTV tubules was first observed in the period 2–4 hr postinfection. Later in the infection cycle, they are seen in close association with viral particles and “virus factories.” Virus specificity of the tubules was demonstrated by specific immune precipitation with antisera against purified virus. There is immunological cross-reaction between BTV and EHDV tubules.