Telomeres are the unique structure at the end of chromosomes,which pose two special challenges for the cellular DNA replication and repair machinery.Because of the inability of lagging strand synthesis to fully replicate a linear template,the chromosome ends is progressively shortening at each replication cycle.The tandem DNA repeats must maintain enough length to allow the cell dividing and mitosing,otherwise the cells would lose the dividing ability and undergo replicative senescence.There are two special pathways to regulate telomere length,which consist of telomerase and alternative lengthening of telomeres(ALT).SUMO is an evolutionarily conserved protein,which is covalently attached to target proteins and alters their conformation,stability,interaction and localization.Currently,a lot of proteins have been proved to be the substrates of SUMOylation.A growing body of evidence implicate that SUMOylation plays a very important role to elongate telomeres in both telomerase and ALT.The Rad5 and Rad52,as well as BLM have been showed either to be modified by SUMO or to interact with SUMO.SUMOylation positively modifies the activity of telomere.
