Evidence of ssDNA in tubulofilamentous particles: their relationship to scrapie-associated fibrils.

Abnormal tubulofilamentous particles were identified by electron microscopy using a simple touch negative staining technique from brains of mice infected with four strains of the scrapie agent. Treatment by three proteolytic enzymes and subsequent treatment with DNase and mung bean nuclease of grids prepared from the infected animals confirmed previous observations that the tubulofilamentous particles observed in scrapie-effected brains are complex structures. The core of the tubulofilamentous particle scrapie-associated fibrils was revealed by treatment with SDS. Treatment with proteolytic enzymes and subsequent treatment with DNase or mung bean nuclease or S1 nuclease also revealed typical and transitional stages of scrapie-associated fibrils. However, treatment with RNase A had no effect. The data suggest that nucleic acid is a single-stranded DNA protected by a protein coat.