H1 does not recognize conventional KHC in rat liver Golgi membranes or in Xenopus egg cytosol. (A) Ubiquitous kinesin immunoprecipitated from solubilized rat liver Golgi membranes using the SUK 4 monoclonal (lanes 1 and 3) was immunoblotted with either polyclonal anti-uKHC (lane 1), which recognized bands at ∼125 and ∼250 kDa (probably incompletely dissociated kinesin heavy chains), or H1 (lane 3), which failed to produce a signal. Nonimmune mouse IgG was used as a control (lanes 2 and 4). The bands between 50 and 60 kDa are antibody heavy chains (lanes 3 and 4). (B) Microtubule pellets enriched in motors were prepared from interphase Xenopus egg cytosol and then extracted with 5 mM ATP and 100 mM NaCl to give an ATP release fraction (lanes 3 and 6) and the remaining microtubule pellet (lanes 2 and 5). Interphase cytosol is loaded in lanes 1 and 4. After SDS-PAGE, protein samples were immunoblotted with either the polyclonal anti-uKHC antibody (lanes 1–3) or the H1 monoclonal antibody (lanes 4–6). Although H1 recognized a band at ∼70 kDa (lane 4), this polypeptide did not pellet with microtubules, unlike uKHC (compare lanes 2 and 3 with 5 and 6).