Meta-Biol

• Pathways

GORASP1 (GRASP65) and GOLGA2 (GM130) form a complex on cis-Golgi membranes. RAB1A or RAB1B, small RAS GTP-ases, can also associate with this complex through interaction with GOLGA2 (Moyer et al. 2001, Weide et al. 2001). GOLGA2 provides a docking site for the USO1 (p115) homodimer (Nakamura et al. 1995, Seeman et al. 2000). RAB1 also participates in this interaction and facilitates it when in the GTP-bound state (Moyer et al. 2001). Binding of USO1 to GORASP1:GOLGA2:RAB1:GTP complex enables fusion of vesicles originating in the endoplasmic reticulum (ER) with cisternae of cis-Golgi.
In mitotic prophase, CDK1 (CDC2) in complex with either CCNB1 (cyclin B1) or CCNB2 (cyclin B2), as both CCNB1 and CCNB2 can localize to Golgi (Jackman et al. 1995, Draviam et al. 2001), phosphorylates GORASP1, GOLGA2 and RAB1 (Bailly et al. 1991, Lowe et al. 1998, Preisinger et al. 2005). Phosphorylation of GOLGA2 and RAB1 impairs their association with USO1, which inhibits thethering and subsequent fusion of ER-originating vesicles with cis-Golgi cisternae, resulting in cessation of ER to Golgi protein trafficking at the start of mitosis and increase in the number of Golgi trafficking vesicles at the expense of Golgi cisternae (Lowe et al. 1998, Seeman et al. 2000, Moyer et al. 2001, Diao et al. 2008).