Proliferating cell nuclear antigen (PCNA) has recently been identified as a target for the binding of several proteins. The cell cycle regulatory protein, p21, and the replication endonuclease, Fen1, have already been described as competing for PCNA binding. Two recent reports have identified DNA (cytosine‐5)methyltransferase (MCMT) and the DNA repair endonuclease XPG as binding to PCNA.^1,2 The remarkable thing about these interactions is that they all seem to occur through a conserved motif that is likely to contact the same site on PCNA. This has fascinating implications for a regulatory network linking these diverse protein functions. BioEssays 20:195–199, 1998. © 1998 John Wiley & Sons, Inc.