Plays an important role in assembly and membrane stacking of the Golgi cisternae, and in the reassembly of Golgi stacks after breakdown during mitosis (PubMed:26363069). 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 (PubMed:16489344). Mediates ER stress-induced unconventional (ER/Golgi-independent) trafficking of core-glycosylated CFTR to cell membrane (PubMed:21884936). 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 (PubMed:26363069). Interacts with the C-terminus of GOLGA2/GM130 under both mitotic and non-mitotic conditions (PubMed:16489344, PubMed:26363069). The interaction is critical for the correct targeting of both proteins to the cis-Golgi. Interacts with TMED2 and TMED3 (By similarity). 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.