Essential for maintaining the architecture of the Golgi stacks and for normal organization of the transitional endoplasmic reticulum (tER). Required for both the formation of the Golgi stacks and the maintenance of the individual cisternae. Associates with the tER membrane (PubMed:12876273). Localizes in developing Golgi stacks (PubMed:11514618). Detected in embryos and larvae (at protein level) (PubMed:12876273). Expressed in larval imaginal disks (at protein level) (PubMed:11514618). RNAi-mediated knockdown results in a loss of Golgi stacks and affects the organization of the transitional ER (tER) sites. Golgi stacks break down and form clusters of vesicles and tubules. The Golgi stacks that are present have an adherent morphology, including a decrease in stack diameter and total cisternae (stacked and single). The tER sites lose their organization and become dispersed throughout the cytoplasm. However, the efficiency of anterograde intracellular transport is not affected. Belongs to the VDP/USO1/EDE1 family.