Involved in the maintenance of Golgi structure by interacting with giantin, affecting protein transport between the endoplasmic reticulum and Golgi (By similarity). Involved in hormone-induced steroid biosynthesis in testicular Leydig cells (PubMed:12711385). Recruits PI4KB to the Golgi apparatus membrane; enhances the enzyme activity of PI4KB activity via its membrane recruitment thereby increasing the local concentration of the substrate in the vicinity of the kinase (By similarity). Homodimer (By similarity). Interacts with the C-terminal cytoplasmic domain of giantin/GOLGB1 (By similarity). Interacts with PBR and PKA regulatory subunit RI-alpha. Does not interact with PKA regulatory subunit RI-beta nor PKA regulatory subunit RII-alpha (PubMed:11731621). Interacts (via Q domain) with PI4KB (via N-terminus) (By similarity). Interacts (via Q domain) with TBC1D22A AND TBC1D22B; interactions with PI4KB and with TBC1D22A and TBC1D22B are mutually exclusive (By similarity). Interacts with C10ORF76 and RAB11B (By similarity). Also mitochondrial (via its interaction with PBR). Expressed in brain (hippocampus, olfactory bulb, neuronal and glial cells of the cortex), eye, submaxillary gland, testis (interstitial and tubular compartments), ovary (granulosa cells, theca cells at late stages and primary follicles), adrenal gland (fasciculata and glomerulosa cells), heart, liver, and steroidogenic cell lines. Present in embryo. Decreases before birth. The central Gln-rich region (Q domain) is involved in binding to PI4KB, TBC1D22A and TBC1D22B (By similarity). The C-terminal GOLD domain is essential for giantin binding. The GOLD domain is also involved in homodimerization (By similarity).