In some cells, strings are the major PrP^Sc store. (A) In some cells, strings are the major PrP^Sc store. ScGT1 were costained with N-terminal mAb 8B4 and core EP1802Y using the FA-denaturing protocol. z-stacks were acquired, images were processed by 3D deconvolution, and three focal planes are shown (see z-values). Images obtained with N- (a–c, red) and core (d–f, green) Abs are superimposed in g–i. The cell has little PrP27-30 in cytoplasmic stores (arrows); most cellular PrP^Sc (including PrP27-30) is in strings and stains with both Abs. (B) An abridged PrP lacking the N terminus can access strings. ScGT1 stably expressing the abridged PrP Δ23-89 version were fixed and costained with mAbs 8B4 (green) and 3F4 (red) with or without prior denaturation with FA (as indicated). 3F4 recognizes Δ23-89 PrP (constructed on the MHM₂ platform) but not endogenous mouse PrP, whereas N-terminal mAb 8B4 does not recognize the abridged Δ23-89 PrP. In some cells, 3F4 codecorated the 8B4 strings (d–f), but only after denaturation (compare b and e), indicating that the abridged PrP are present in strings in their PrP^Sc form. N-proximal sequences are thus not necessary (in cis) to guide PrP to strings.