Accepts the ubiquitin-like proteins SUMO1, SUMO2 and SUMO3 from the UBLE1A-UBLE1B E1 complex and catalyzes their covalent attachment to other proteins with the help of an E3 ligase such as RANBP2, CBX4 and ZNF451 (By similarity). Can catalyze the formation of poly-SUMO chains (By similarity). Essential for nuclear architecture and chromosome segregation (By similarity). Necessary for sumoylation of FOXL2 and KAT5 (By similarity). Sumoylates p53/TP53 at 'Lys-386' (By similarity). Mediates sumoylation of ERCC6 which is essential for its transcription-coupled nucleotide excision repair activity (By similarity). Protein modification; protein sumoylation. Forms a complex with SENP6 and UBE2I in response to UV irradiation (By similarity). Forms a tight complex with RANGAP1 and RANBP2 (By similarity). Identified in a complex with SUMO2 and UBE2I, where one ZNF451 interacts with one UBE2I and two SUMO2 chains, one bound to the UBE2I active site and the other to another region of the same UBE2I molecule (By similarity). Interacts with SETX (By similarity). Interacts with HIPK1 and HIPK2 (By similarity). Interacts with PPM1J (By similarity). Interacts with RASD2 (By similarity). Interacts with TCF3 (By similarity). Interacts with NR2C1; the interaction promotes its sumoylation (By similarity). Interacts with SIAH1 (By similarity). Interacts with PARP (By similarity). Interacts with various transcription factors such as TFAP2A, TFAP2B, and TFAP2C (By similarity). Interacts with AR (By similarity). Interacts with ETS1 (By similarity). Interacts with SOX4 (By similarity). Interacts with RWDD3; the interaction enhances the sumoylation of a number of proteins such as HIF1A and I-kappa-B (By similarity). Interacts with FOXL2 (By similarity). Interacts with DNM1l (via its GTPase and B domains); the interaction promotes sumoylation of DNM1L, mainly in its B domain (By similarity). Interacts with NFATC2IP; this inhibits formation of poly-SUMO chains (By similarity). Interacts with FHIT (By similarity). Interacts with PRKRA and p53/TP53 (By similarity). Interacts with UHRF2 (By similarity). Interacts with NR3C1 and this interaction is enhanced in the presence of RWDD3 (By similarity). Interacts with MTA1 (By similarity). Interacts with ZNF451 (By similarity). Interacts with CPEB3 (By similarity). Interacts with SUMO1, SUMO2, and SUMO3 (By similarity). Interacts with IPO13 (By similarity). Interacts with DNMT1 (By similarity). Mainly nuclear (By similarity). In spermatocytes, localizes in synaptonemal complexes (By similarity). Recruited by BCL11A into the nuclear body (By similarity). Phosphorylation at Ser-71 significantly enhances SUMOylation activity. Belongs to the ubiquitin-conjugating enzyme family.