PCNASUMO and Srs2:: a model SUMO substrate-effector pair

Attachment of the SUMO (small ubiquitin-related modifier) to the replication factor PCNA (proliferating-cell nuclear antigen) in the budding yeast has been shown to recruit a helicase, Srs2, to active replication forks, which in turn prevents unscheduled recombination events. In the present review, I will discuss how the interaction between SUMOylated PCNA and Srs2 serves as an example for a mechanism by which SUMO modulates the properties of its targets and mediates the activation of downstream effector proteins.