trans-Golgi network membrane
RAB proteins are required for the RINT-1/ZW10 and COG-dependent organization of the Golgi ribbon stack, and for the trafficking of proteins through the Golgi. Indeed, cargo traffic through the Golgi depends on the maintenance of the Golgi stacks (Hirose et al, 2004; Arasaki et al, 2006; Sun et al, 2007; reviewed in Liu and Storrie, 2015). RAB6 is the primary RAB protein involved in intra-Golgi trafficking; it also has roles in COPI-independent retrograde traffic from the Golgi to the ER. RAB6A is a widely expressed isoform, while RAB6B is restricted to neuronal tissue (Darchen and Goud, 2000). RAB6 is localized to the trans-Golgi network (TGN), and a GTP-locked constitutively active form induces concentration of Golgi enzymes into the ER (Ferrano et al, 2104; Jiang and Storrie, 2005; Martinex et al, 1997; Micaroni et al, 2013; Storrie et al, 2012; Sun et al, 2007; Young et al, 2005). Inactive RAB6:GDP is recruited to the TGN through interaction with the RIC1:RGP1 complex, which also acts as a guanine nucleotide exchange factor (GEF) for RAB6 (Pusapati et al, 2012; Siniossoglou et al, 2000; Siniossoglou et al, 2001).