FIG. 1.

Organization of the pCMV2JS₂₁ construct and in vitro synthesis of JSRV₂₁ particles. (a) pCMV2JS₂₁ is a plasmid containing a modified version of the integrated JSRV₂₁ provirus in which the U3 region of the upstream LTR was replaced by the human cytomegalovirus immediate-early promoter. (b) SDS-PAGE and Western blotting of 300-fold-concentrated supernatant from 293T cells transiently transfected with pCMV2JS₂₁. The filters were probed with a rabbit polyclonal antiserum toward the major capsid protein (CA) of JSRV. Lung fluid collected from an SPA-affected animal and concentrated in the same way as the 293T supernatant was used as a positive control (LF). Concentrated supernatant from mock-transfected 293T cells was used as a negative control (M). The 26-kDa JSRV-CA protein is indicated.