REV1 is a deoxycytidyl transferase that belongs to the DNA polymerase type-Y family. REV1 was cloned as the human homolog of yeast REV1. Similar to its yeast counterpart, REV1 binds damaged DNA, with the preferred substrate being DNA with an AP (abasic - apurinic/apyrimidinic) site. The mechanism for DNA damage recognition has not been elucidated (Lin et al. 1999, Gibbs et al. 2000). Besides DNA binding, REV1 has a ubiquitin binding motif in its C-terminal domain that interacts with monoubiquitinated PCNA, which enhances REV1-mediated translesion synthesis (Garg and Burgers 2005, Wood et al. 2007).