Together with PML, this tumor suppressor is a major constituent of the PML bodies, a subnuclear organelle involved in a large number of physiological processes including cell growth, differentiation and apoptosis. Functions as a transcriptional coactivator of ETS1 and ETS2. Under certain conditions, it may also act as a corepressor of ETS1 preventing its binding to DNA. Through the regulation of ETS1 it may play a role in angiogenesis, controlling endothelial cell motility and invasion. Through interaction with the MRN complex it may be involved in the regulation of telomeres lengthening. May also regulate TP53-mediated transcription and through CASP8AP2, regulate FAS-mediated apoptosis. May also play a role in infection by viruses through mechanisms that may involve chromatin and/or transcriptional regulation (By similarity). Homodimer. Interacts with members of the HP1 family of nonhistone chromosomal protein, such as CBX5 and CBX3 via the PxVxL motif. Interacts with ETS1; the interaction is direct and modulates ETS1 transcriptional activity. Interacts with the MRN complex which is composed of two heterodimers RAD50/MRE11 associated with a single NBN; recruits the complex to PML-related bodies. Interacts with HIPK2; positively regulates TP53-dependent transcription. Interacts with CASP8AP2; may negatively regulate CASP8AP2 export from the nucleus to the cytoplasm (By similarity). Accumulates in the cytoplasm upon FAS activation. By interferon. The HSR domain is important for the nuclear body targeting as well as for the dimerization. Contains one Pro-Xaa-Val-Xaa-Leu (PxVxL) motif, which is required for interaction with chromoshadow domains. This motif requires additional residues -7, -6, +4 and +5 of the central Val which contact the chromoshadow domain. Sumoylated. Sumoylated with SUMO1. Sumoylation depends on a functional nuclear localization signal but is not necessary for nuclear import or nuclear body targeting. Sumoylation may stabilize the interaction with CBX5 (By similarity). Sp100 is a single-copy gene. A related gene, D1LUB1/Sp100-rs, occurs in multiple copies and forms a conspicuous cluster in the chromosome 1. Sp100 and D1LUB1/Sp100-rs are homologous from the promoter up to a position in intron 3, but they differ 3' of that position.