Plays an important role in assembly and membrane stacking of the Golgi cisternae, and in the reassembly of Golgi stacks after breakdown during mitosis. Key structural protein required for the maintenance of the Golgi apparatus integrity: its caspase-mediated cleavage is required for fragmentation of the Golgi during apoptosis (By similarity). Also mediates, via its interaction with GOLGA2/GM130, the docking of transport vesicles with the Golgi membranes (By similarity). Mediates ER stress-induced unconventional (ER/Golgi-independent) trafficking of core-glycosylated CFTR to cell membrane (By similarity). Homodimer. Forms higher-order oligomers under interphase but not mitotic conditions. Dimers of the protein on one membrane might be able to interact with dimers on another and so stack cisternae. Interacts with the C-terminus of GOLGA2/GM130 under both mitotic and non-mitotic conditions. The interaction is critical for the correct targeting of both proteins to the cis-Golgi. Interacts with TMED2 and TMED3. Phosphorylated by CDC2/B1 and PLK kinases during mitosis. Phosphorylation cycle correlates with the cisternal stacking cycle. Phosphorylation of the homodimer prevents the association of dimers into higher-order oligomers, leading to cisternal unstacking. Target for caspase-3 cleavage during apoptosis. The cleavage contributes to Golgi fragmentation and occurs very early in the execution phase of apoptosis. Myristoylated. Belongs to the GORASP family.