Figure 4.

A 3D-rendering of couples of compartments (A–F). (A) The model shown in Figure 3B was rotated by 90° on the x-axis, partially clipped and enlarged. By this perspective, coiled coils are seen from one of their extremity. Magnification is high enough to glimpse a small eyelet at the center of one coiled coil (white circle) which corresponds to the axis around which the α helices wrap around each other. Magnification bar, 120 nm. (B–C) The compartments shown in A have been isolated. The eyelets (white circles) marking the central axis of the α helices are numerous. Vertical and lateral connecting tubules can be appreciated departing from the α helices. Magnification bar, 120 nm. (D) The model shown in A was tilted by 10° so that coiled coils, cut transversely (white circles), are now aligned along x planes. In this way, vertical connecting tubules are not perpendicular to coiled coils and lateral connecting tubules but they form an 80° angle. Magnification bar, 120 nm. (E) A single coiled coil has been isolated clipping the model shown in Figure 3A. The two α helices of the yellow and red compartments can be seen twisting around each other. Vertical connecting tubules (vct) and lateral connecting tubules (lct) are also visible arising at regular distance from the α helices. Magnification bar, 120 nm. (F) A single coiled coil formed by the green and purple compartments has been isolated clipping the model shown in Figure 3B. The same notes made for E also apply here. Magnification bar 120 nm. Intertubular filamentous framework (G–I). Delicate filamentous strands tether tubular compartment one to the other. Several examples are shown in encompassed between the black arrowheads. In some cases strands (encompassed by double black arrowheads) seems to be longer because they tether more distant tubules (H–I). Monkey 10026. Magnification bars, 60 nm.