Kinesin‐1 (uKHC/KIF5B) is Required for Bidirectional Motility of ER Exit Sites and Efficient ER‐to‐Golgi Transport

Transport of proteins and lipids between intracellular compartments is fundamental to the organization and function of eukaryotic cells. The efficiency of this process is greatly enhanced through coupling of membranes to microtubules. This serves two functions, organelle positioning and vesicular transport. In this study, we show that in addition to the well‐known role for the minus‐end motor dynein in endoplasmic reticulum (ER)‐to‐Golgi transport, the plus‐end‐directed motor kinesin‐1 is involved in positioning coat protein II‐coated ER exit sites (ERES) in cells as well as the formation of transport carriers and their movement to the Golgi. Using two‐dimensional Gaussian fitting to determine their location at high spatial resolution, we show that ERES undergo short‐range bidirectional movements. Bidirectionality depends on both kinesin‐1 and dynein. Suppression of kinesin‐1 (KIF5B) also inhibits ER‐to‐Golgi transport and affects the morphology of ER‐to‐Golgi transport carriers. Furthermore, we show that suppression of dynein heavy chain expression increases the range of movement of ERES, suggesting that dynein might anchor ERES, or the ER itself, to microtubules. These data implicate kinesin‐1 in the spatial organization of the ER/Golgi interface as well as in traffic outside the ER.