Figure 3.

Surface representations of the 3-D density maps. (A and B) The maps were computed from averaged data (see Figure 2) for 15-protofilament brain microtubules decorated with dimeric kinesin in the absence of free nucleotide (A) or in the presence of ADP (B). They are in the standard orientation, with the microtubule plus end at the top of the page. (C and D) Enlarged views of individual dimeric motors are shown. In each case, H1 is the directly bound head; H2 is the tethered head. An arrow indicates the absence in the nucleotide-free structure (C) of a feature in the ADP-containing structure (D) that can fit loop L12 (see Figure 6c).