Figure 3. The proximal and distal centriole show several major structural differences.

(a) The proximal centriole was characterized by complete triplet microtubules that showed strong density for both parts of the A-C linker (white double arrowheads) and the pinhead (green arrow). (b) In contrast, the distal centriole lacked the A-C linker (white double arrowheads) and instead of a pinhead, the distal map had a density (green arrow) that extended out from the A-tubule. (c) A merge of the distal and proximal maps highlighted the differences between them, with differences at the inner AB-junction (white arrow) being the most obvious. (d) A zoomed in view of the A-tubule in the proximal centriole showed two MIPs, one straddling protofilaments A09 and A10, the other binding to A11. Note that the inner AB-junction is compact (dashed white circle). (e) A zoomed in view of the A-tubule in the distal centriole also showed a MIP straddling protofilaments A09-A10, but the proximal centriole lacked the A11-bound MIP. Here the inner AB-junction was more elaborate and formed the platform from which densities extended (dashed white circle). (f) A merged view of both A-tubules allows the differences at the inner AB-junction to be fully appreciated. Scale bars are 25 nm.