E2F/DP complexes play a pivotal role in the regulation of the G1/S transition in animals. Recently, plant E2F homologs have been cloned, but DP-related sequences have not been identified so far. Here we report that Arabidopsis thaliana contains at least two different DP-related genes, AtDPa and AtDPb. They exhibit an overall domain organization similar to that of their animal counterparts, although phylogenetic analysis demonstrated that they form a separate subgroup. AtDPs efficiently heterodimerize in vitro with the Arabidopsis E2F-related proteins, AtE2Fa and AtE2Fb through their dimerization domains. AtDPa and AtE2Fa are predominantly produced in actively dividing cells with highest transcript levels in early S phase cells.