KINESIN IS THE MOTOR FOR MICROTUBULE-MEDIATED GOLGI-TO-ER MEMBRANE TRAFFIC

The distribution and dynamics of both the ER and Golgi complex in anim al cells are known to be dependent on microtubules; in many cell types the ER extends toward the plus ends of microtubules at the cell perip hery and the Golgi clusters at the minus ends of microtubules near the centrosome. In this study we provide evidence that the microtubule mo tor, kinesin, is present on membranes cycling between the ER and Golgi and powers peripherally directed movements of membrane within this sy stem. Immunolocalization of kinesin at both the light and electron mic roscopy levels in NRK cells using the H1 monoclonal antibody to kinesi n heavy chain, revealed kinesin to be associated with all membranes of the ER/Golgi system. At steady-state at 37 degrees C, however, kinesi n was most concentrated on peripherally distributed, pre-Golgi structu res containing beta COP and vesicular stomatitis virus glycoprotein ne wly released from the ER. Upon temperature reduction or nocodazole tre atment, kinesin's distribution shifted onto the Golgi, while with bref eldin A (BFA)-treatment, kinesin could be found in both Golgi-derived tubules and in the ER. This suggested that kinesin associates with mem branes that constitutively cycle between the ER and Golgi. Kinesin's r ole on these membranes was examined by microinjecting kinesin antibody . Golgi-to-ER but not ER-to-Golgi membrane transport was found to be i nhibited 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 Golg i complex.