Is believed to be a multifunctional and multicompartmental protein involved in inflammation and infection processes, ribosome biogenesis, protein synthesis in mitochondria, regulation of apoptosis, transcriptional regulation and pre-mRNA splicing. At the cell surface is thought to act as an endothelial receptor for plasma proteins of the complement and kallikrein-kinin cascades. Putative receptor for C1q; specifically binds to the globular 'heads' of C1q thus inhibiting C1; may perform the receptor function through a complex with C1qR/CD93. In complex with cytokeratin-1/KRT1 is a high affinity receptor for kininogen-1/HMWK. Can also bind other plasma proteins, such as coagulation factor XII leading to its autoactivation. May function to bind initially fluid kininogen-1 to the cell membrane. The secreted form may enhance both extrinsic and intrinsic coagulation pathways. It is postulated that the cell surface form requires docking with transmembrane proteins for downstream signaling which might be specific for a cell-type or response. By acting as C1q receptor is involved in chemotaxis of immature dendritic cells and neutrophils and is proposed to signal through CD209/DC-SIGN on immature dendritic cells, through integrin alpha-4/beta-1 during trophoblast invasion of the decidua, and through integrin beta-1 during endothelial cell adhesion and spreading. Signaling involved in inhibition of innate immune response is implicating the PI3K-AKT/PKB pathway. Required for protein synthesis in mitochondria. In mitochondrial translation may be involved in formation of functional 55S mitoribosomes; the function seems to involve its RNA-binding activity. May be involved in the nucleolar ribosome maturation process; the function may involve the exchange of FBL for RRP1 in the association with pre-ribosome particles. Involved in regulation of RNA splicing by inhibiting the RNA-binding capacity of SRSF1 and its phosphorylation. Is required for the nuclear translocation of splicing factor U2AF1L4. Involved in regulation of CDKN2A- and HRK-mediated apoptosis. May be involved in regulation of FOXC1 transcriptional activity and NFY/CCAAT-binding factor complex-mediated transcription. May play a role in antibacterial defense. Homotrimer; three monomers form a donut-shaped structure with an unusually asymmetric charge distribution on the surface. Interacts with CDK13, HRK, VTN, NFYB, ADRA1B, FOXC1, DDX21, DDX50, NCL, SRSF1 and SRSF9. Interacts with CD93; the association may represent a cell surface C1q receptor. Interacts with KRT1; the association represents a cell surface kininogen receptor. Interacts with CD209; the interaction is indicative for a C1q:C1QBP:CD209 signaling complex. Interacts with FBL and RRP1; the respective interactions with C1QBP are competitive. Probably associates with the mitoribosome. Interacts with MAVS; the interaction occurs upon viral transfection. Interacts with PPIF. Interacts with U2AF1L4. Interacts with PLEKHN1. Interacts with VGF-derived peptide TLQP-21 (By similarity). Seems to be predominantly localized to mitochondria. Secreted by activated lymphocytes. Belongs to the MAM33 family.