Small ubiquitin-like modifier(SUMO)proteins 1,2 and 3 can be covalently conjugated to specific lysine residues on target proteins in a process dubbed SUMOylation.This conserved posttranslational modification that was reported for the first time in 1996 has emerged as an important regulatory mechanism in cell physiology,especially in nuclear signaling,transport,transcription and DNA replication/repair[1,2].