Evidence that scrapie-associated tubulofilamentous particles contain a single-stranded DNA

Unique virus-like tubulofilamentous particles, termed nemavirus, have been consistently observed in spongiform encephalopathic brains by electron microscopy in thin sections. Sodium dodecyl sulphate treatment of unfixed infected brain tissue on grids revealed a twisted fibril core of tubulofilamentous particles. The unmasked fibrils were identified as scrapie-associated fibrils by immunogold labelling. Both tubulofilamentous particles and scrapie-associated fibrils are not artefacts of protease treatment of protein formed in vitro during purification. Treatment with protease and nucleases revealed that each tubule consists of three layers: (i) an outer coat of protease-sensitive material; (ii) an intermediate layer that is digested by DNase and mung bean nuclease, and (iii) inner protease-resistant protein scrapie-associated fibril.