FIG. 2.

Electron micrographs of rotary-shadowed KPR₁₃₀ molecules. These images, together with previous studies¹³, are consistent with the hypothesis that a KRP₁₃₀ holoenzyme comprises four 130K subunits assembled into a structure 96 nm long, with a total M_r of roughly 500K, Stokes radius of 16.2 nm, and S-value of 7.6 S. For comparison, kinesin comprises two heavy chains of 110K–130K and two light chains of 55K–80K assembled into a structure 75–80 nm long with a total M_r of 350K–400K, Stokes radius of 9nm, and S-value of 9.0–9.6S. The dimensions of both rotary-shadowed KRP₁₃₀ and kinesin appear slightly larger than their true dimensions owing to the coating of platinum, which in our experiments is routinely estimated to be approximately 2.5 nm thick.

METHODS. KRP₁₃₀ alone or KRP₁₃₀–MT complexes were mixed with an equal volume of 80% glycerol containing 0.6–1.0 M ammonium acetate and sprayed onto freshly cleaved mica plates. The plates were then vacuum dried, rotary shadowed with platinum at a 6° angle using a Balzers BAF 400T freeze-fracture device, and processed as described previously²⁸. The replicas were visualized on a Philips 410LS electron microscope at 80 kV. No difference in the structure of KRP₁₃₀ was observed with or without the MT binding step.