The Golgi apparatus is a highly complex organelle comprised of a stack of cisternal membranes on the secretory pathway from the ER to the cell surface. The structure is maintained by an exoskeleton or Golgi matrix constructed from a family of coiled-coil protein, the golgins and other peripheral membrane components such as GRASP55 and GRASP65 (1). GRASP55 (Golgi reassembly stacking protien or p59) is a component of the Golgi stacking machinery. GRASP55 is highly homologous to GRASP65 and contains two PDZ domains. GRASP55 is myristoylated and palmitoylated. Unlike GRASP65, GRASP55 does not have detectable binding with the vesicle docking protein GM130 and is located on the medial-Golgi rather than cis-Golgi. Both GRASP55 and GRASP65 function in the stacking of Golgi Cisternae (2,3). The novel coiled-coil protein golgin 45 interacts with GRASP55 and the GTP form of Rab 2, suggesting that GRASP55 and golgin 45 form a Rab 2 effector complex on medial-Golgi essential for normal protein transport and Golgi structure (4). ERK2 directly phosphorylates GRASP55, which is phosphorylated in mitotic cells, suggesting that mitogen-activated protein kinase kinase (MKK)/ERK pathway phosphorylates the Golgi during mitosis (5). Function: May be involved in assembly and membrane stacking of the Golgi cisternae, and in the process by which Golgi stacks reform after mitotic breakdown. May regulate the intracellular transport and presentation of a defined set of transmembrane proteins, such as transmembrane TGFA. Subcellular Location: Golgi apparatus membrane. Post-translational modifications: Myristoylated. Myristoylation is essential for the Golgi targeting. Palmitoylated. Phosphorylated in mitotic cells. Similarity: Belongs to the GORASP family. Contains 1 PDZ (DHR) domain. SWISS: Q9H8Y8 Gene ID: 26003 Database links: Entrez Gene: 26003 Human Entrez Gene: 70231 Mouse Omim: 608693 Human SwissProt: Q9H8Y8 Human SwissProt: Q99JX3 Mouse Unigene: 431317 Human Unigene: 271950 Mouse Unigene: 470827 Mouse