The small ubiquitin-like modifier-1 (SUMO-1) consensus sequence mediates Ubc9 binding and is essential for SURIO-1 modification

SUMO-1 is an ubiquitin-related protein that is covalently conjugated to a d iverse assortment of proteins. The consequences of SUMO-1 modification incl ude the regulation of protein-protein interactions, protein-DNA interaction s, and protein subcellular localization. At present, very little is underst ood about the specific mechanisms that govern the recognition of proteins a s substrates for SUMO-1 modification. However, many of the proteins that ar e modified by SUMO-1 interact directly with the SUMO-1 conjugating enzyme, Ubc9, These interactions suggest that Ubc9 binding may play an important ro le in substrate recognition as well as in substrate modification. The SUMO- 1 consensus sequence (SUMO-1-CS) is a motif of conserved residues surroundi ng the modified lysine residue of most SUMO-1 substrates. This motif confor ms to the sequence "Psi KXE," where Psi is a large hydrophobic residue, K i s the lysine to which SUMO-1 is conjugated, X is any amino acid, and E is g lutamic acid. In this study, we demonstrate that the SUMO-1-CS is a major d eterminant of Ubc9 binding and SUMO-1 modification. Mutating residues in th e SUMO-1-CS abolishes both Ubc9 binding and substrate modification. These f indings have important implications for how SUMO-1 substrates are recognize d and for how SUMO-1 is ultimately transferred to specific lysine residues on these substrates.