The distribution and dynamics of both the ER and Golgi complex in animal cells are known to be dependent on microtubules; in many cell types the ER extends toward the plus ends of microtubules at the cell periphery and the Golgi clusters at the minus ends of microtubules near the centrosome. In this study we provide evidence that the microtubule motor,
kinesin, is present on membranes cycling between the ER and Golgi and powers peripherally directed movements of membrane within this system. Immunolocalization of
kinesin at both the light and electron microscopy levels in NRK cells using the H1
monoclonal antibody to
kinesin heavy chain, revealed
kinesin to be associated with all membranes of the ER/Golgi system. At steady-state at 37 degrees C, however,
kinesin was most concentrated on peripherally distributed, pre-Golgi structures containing
beta COP and
vesicular stomatitis virus
glycoprotein newly released from the ER. Upon temperature reduction or
nocodazole treatment,
kinesin's distribution shifted onto the Golgi, while with
brefeldin A (BFA)-treatment,
kinesin could be found in both Golgi-derived tubules and in the ER. This suggested that
kinesin associates with membranes that constitutively cycle between the ER and Golgi.
Kinesin's role on these membranes was examined by microinjecting
kinesin antibody. Golgi-to-ER but not ER-to-Golgi membrane transport was found to be inhibited by the microinjected anti-
kinesin, suggesting
kinesin powers the microtubule plus end-directed recycling of membrane to the ER, and remains inactive on pre-Golgi intermediates that move toward the Golgi complex.