Buoyant-density and transmission electron micrograph analysis of ENA tumor homogenate. (A) 20 to 80% (wt/wt) sucrose gradient isopycnic centrifugation of the original ENA inoculum and a preparation of cell free tumor homogenate from the experimentally induced nasal tumor. The RT activity (solid lines) and density (dashed line) of each of the ten fractions is shown. (B) Immunoblot analysis for ENTV-1 capsid protein in fractions one through ten. ENA inoculum was loaded as a positive control for capsid (lane C). (C) Transmission electron micrograph analysis of fractions six and seven of the ENA inoculum (left) and cell free tumor homogenate from the experimentally induced nasal tumor (Expt ENA; right) showing virus particles with typical betaretrovirus morphology.