Figure 3(A) (Top) 2D slice through STA transverse view of T. spp. microtubule triplet, with insets showing position of pinhead (dashed green box) and A-C linker (dashed red box). (Bottom) Longitudinal 2D slice of STA centered on the pinhead (left) or A-C linker (right). (B) Transverse view of T. spp. microtubule triplet STA. Microtubule protofilament numbers are indicated, as are the pinhead and A-C linker (only the C-link is visible; the A-link lies on the edge of the volume and is thus less well resolved in this STA -for better view see STA centered on A-C linker in (D)). Prominent microtubule inner densities within the A-microtubule are highlighted (empty arrowhead next to A9, chevron next to A5), as are additional external densities at the A-B and B-C inner junctions (black arrowheads). Double arrowheads point to viewing direction in indicated panels. (C) Longitudinal view of T. spp. STA centered on the pinhead from the viewing point indicated in (B). The pinfeet (PinF1 and PinF2) and pinbody (PinB) are indicated, as are microtubule protofilaments A3 and A4. The average distance between pinfeet elements is 8.6 ± 0.4 nm and 7.9 ± 0.4 nm (N=3 each). Corresponding transverse views are shown below, illustrating the connection of PinF2 with protofilament A3. (D) Longitudinal view of T. spp. STA centered on the A-C linker from the viewing point indicated in (B). Microtubule protofilaments A8/9 and C9/C10 of two adjacent triplets are indicated, as are the connected A- and C-links. The average distance between A- and C-links is 8.4 ± 0.4 nm and 8.4 ± 0.3 nm (both N=6). Corresponding transverse views are shown below, chevrons point to connection. (E) (Top) 2D slice through STA transverse view of T. agilis microtubule triplet, with insets showing position of pinhead (dashed green box) and A-C linker (dashed red box). (Bottom) Longitudinal 2D slice of STA centered on the pinhead (left) or A-C linker (right). (F) Transverse view of T. agilis microtubule triplet STA. Microtubule protofilament numbers are indicated, as are the pinhead and A-C linker (only the C-link is visible; the A-link lies on the edge of the volume and is thus less well resolved in this STA -for better view see STA centered on A-C linker in (H)). Prominent microtubule inner densities (MIPs) within the A-microtubule are highlighted (empty arrowhead next to A9), as are additional external densities at the A-B and B-C inner junctions (black arrowheads). Double arrowheads point to viewing direction in indicated panels. (G) Longitudinal view of T. agilis STA centered on the pinhead from the viewing point indicated in (F). The pinfeet (PinF1 and PinF2) and pinbody (PinB) are indicated, as are microtubule protofilaments A3/A4. The average distance between pinfeet elements is 8.4 ± 0 nm in each case (both N=3). Corresponding transverse views are shown below, illustrating the connection of PinF2 with protofilament A3. (H) Longitudinal view of T. agilis STA centered on the A-C linker from the viewing point indicated in (F). Microtubule protofilaments A8/9 and C9/C10 of two adjacent triplets are indicated, as are the connected A- and C-links. The average distance between A- and C-links is 8.4 ± 0.3 nm and 8.4 ± 0.9 nm (N=6 and N=5, respectively). Corresponding transverse views are shown below, chevrons point to connection; the connection of the A-link with A9 is only partially visible in the transverse view at this height, as indicated by the dashed chevron.