Cx37-HKKSL localized to the ER and Golgi apparatus. HeLa cells transfected with Cx37-HKKSL were fixed, permeabilized and then immunolabeled for Cx37 (a, d; red) and an ER marker, protein sulfide isomerase (PDI) (b, green) or a marker for the cis Golgi apparatus (GM130) (e, green). Merged images are shown in (c, f). Most Cx37-HKKSL colocalized with PDI, consistent with ER localization. A small fraction of Cx37-HKKSL colocalized with GM130, suggesting low levels of transport to the cis aspect of the Golgi apparatus. Bar 10 µm