A small ubiquitin-related polypeptide involved in targeting RanGAP1 to nuclear pore complex protein RanBP2

SUMO-1, a novel peptide of 101 amino acids, has been found to be covalently linked to the mammalian Ran GTPase-activating protein RanGAP1 in an adenosine triphosphate-dependent reaction. SUMO-1 exhibits a homology to ubiquitin, a 76-residue protein found in eukaryotes. Data indicate that the polypeptide is involved in protein targeting and not degradation. At least three additional intranuclear proteins are modified with SUMO-1 or with a protein closely resembling it.