Inhibits PIK3C3 activity; under basal conditions negatively regulates PI3K complex II (PI3KC3-C2) function in autophagy. Negatively regulates endosome maturation and degradative endocytic trafficking and impairs autophagosome maturation process (PubMed:19270693). Can sequester UVRAG from association with a class C Vps complex (possibly the HOPS complex) and negatively regulates Rab7 activation (By similarity). Involved in regulation of pathogen-specific host defense of activated macrophages. Following bacterial infection promotes NADH oxidase activity by association with CYBA thereby affecting TLR2 signaling and probably other TLR-NOX pathways. Stabilizes the CYBA:CYBB NADPH oxidase heterodimer, increases its association with TLR2 and its phagosome trafficking to induce antimicrobial burst of ROS and production of inflammatory cytokines. Following fungal or viral infection (implicating CLEC7A (dectin-1)-mediated myeloid cell activation or DDX58/RIG-I-dependent sensing of RNA viruses) negatively regulates pro-inflammatory cytokine production by association with CARD9 and sequestering it from signaling complexes (By similarity). Associates with PI3K (PI3KC3/PI3K-III/class III phosphatidylinositol 3-kinase) complex II (PI3KC3-C2) in which the core composed of the catalytic subunit PIK3C3, the regulatory subunit PIK3R4 and BECN1 is associated with UVRAG; in the complex interacts directly with PI3KC3 and UVRAG (PubMed:19270693). Interacts with Rab7 (RAB7A or RAB7B) (GTP-bound form); Rab7 and UVRAG compete for RUBCN binding; can interact simultaneously with Rab7 and the PI3K complex. Interacts with CYBA and CYBB; indicative for the association with the CYBA:CYBB NADPH oxidase heterodimer. Interacts with NOX4 and probably associates with the CYBA:NOX4 complex. Interacts with YWHAB and CARD9 in a competitive and stimulation-dependent manner; RUBCN exchanges interaction from YWHAB to CARD9 upon stimulation with beta-1,3-glucan (By similarity). Predominantly located in late endosomes/lysosomes, only partially detected in early endosome and not at all in the Golgi apparatus. Extended N-terminus. Extended N-terminus.