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. 1998 Jun 23;95(13):7299–7304. doi: 10.1073/pnas.95.13.7299

Figure 1.

Figure 1

Frozen-hydrated images of immature, protease-deficient (PR−) (a, b) and mature, wild-type (WT) (c) MuLV particles. Both particle types are bounded by a lipid bilayer envelope (E) and display a variation in diameter. The inner membrane leaflet was thicker than the outer leaflet, which we attribute at least in part to the matrix protein (M). Both particles displayed a core region (C), which was rounded in the PR− MuLV and polygonal in the WT MuLV. The surface of the core in the PR− MuLV displayed a characteristic track-like structure (T). Occasionally, a second inner track (IT) could be identified that was concentric or continuous with the outer fringe. Rotavirus particles (labeled RV) (≈1,000 Å diameter) retained their constant diameter and spherical shape during ultracentrifugation with the PR− MuLV (d) and WT MuLV (e).