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. Can sequester UVRAG from association with a class C Vps complex (possibly the HOPS complex) and negatively regulates Rab7 activation (PubMed:20974968, PubMed:21062745). 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 (PubMed:22423966). 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 (PubMed:22423967). 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:19270696, PubMed:21062745). 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 (PubMed:20943950, PubMed:20974968, PubMed:21062745). 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 (PubMed:22423966). 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 (PubMed:22423967). Predominantly located in late endosomes/lysosomes, only partially detected in early endosome and not at all in the Golgi apparatus. The disease is caused by variants affecting the gene represented in this entry. Extended N-terminus.