Analysis of Rab18 and Rab3GAP localization to the ER. (a) Western blot of COS7 control cells and COS7 cells expressing GFP-Rab18 with antibodies to endogenous Rab18 and GFP. (b) GFP-Rab18, reticulon 4 (Rtn4), and CLIMP-63 staining is shown in COS7 cells. (c) Calnexin staining and mCherry (mCh)-tagged Rab18 are shown in HeLa cells. (d) COS7 cells expressing GFP-Rab18 were stained for Rab3GAP1 and markers for COP I (β-COP), COP II (Sec31), ERGIC-53, and LAMP1. Arrowheads in the enlarged region show details of Rab3GAP1 localization to ER tubules marked by GFP-Rab18. (e) The enlarged region corresponding to the yellow boxed area in d shows details of the Rab3GAP1 and different compartment markers. Bars are marked in the figure.