Role of Xklp3, a subunit of the Xenopus kinesin II heterotrimeric complex,in membrane transport between the endoplasmic reticulum and the Golgi apparatus

The function of the Golgi apparatus is to modify proteins and lipids synthe sized in the ER and sort them to their final destination, The steady-state size and function of the Golgi apparatus is maintained through the recyclin g of some components back to the ER, Several lines of evidence indicate tha t the spatial segregation between the ER and the Golgi apparatus as well as trafficking between these two compartments require both microtubules and m otors. We have cloned and characterized a new Xenopus kinesin like protein, Xklp3, a subunit of the heterotrimeric Kinesin II. By immunofluorescence i t is found in the Golgi region. A more detailed analysis by EM shows that i t is associated with a subset of membranes that contain the KDEL receptor a nd are localized between the ER and Golgi apparatus. An association of Xklp 3 with the recycling compartment is further supported by a biochemical anal ysis and the behavior of Xklp3 in BFA-treated cells. The function of Xklp3 was analyzed by transfecting cells with a dominant-negative form lacking th e motor domain. In these cells, the normal delivery of newly synthesized pr oteins to the Golgi apparatus is blocked. Taken together, these results ind icate that Xklp3 is involved in the transport of tubular-vesicular elements between the ER and the Golgi apparatus.