E3 SUMO-protein ligase which facilitates SUMO1 and SUMO2 conjugation by UBE2I. Involved in transport factor (Ran-GTP; karyopherin)-mediated protein import via the F-G repeat-containing domain which acts as a docking site for substrates. Binds single- stranded RNA (in vitro). May bind DNA. Component of the nuclear export pathway. Specific docking site for the nuclear export factor exportin-1. Sumoylates PML at 'Lys-490' which is essential for the proper assembly of PML-NB. {ECO:0000269|PubMed:11792325; ECO:0000269|PubMed:12032081; ECO:0000269|PubMed:15378033; ECO:0000269|PubMed:15931224; ECO:0000269|PubMed:22194619}.