SUMO (Small Ubiquitin-like Modifier) is a post-translational modifier, which is conjugated to its targets through a pathway analogous to that of ubiquitinylation. SUMO is implicated in a variety of cellular processes that have consequences for the repair of DNA damage and cell cycle progression. This is reflected in the fact that S. pombe cells, mutant for the SUMO conjugation pathway, are sensitive to genotoxins and have aberrant cellular morphologies and defects in DNA segregation.