Human DOC-1/CDK2AP1 gene encodes a growth suppressor protein of 12kDa (p12DOC-1=CDK2AP1). Recently, p12DOC-1=CDK2AP1 has been shown to associate with cell cycle proteins including CDK2 and DNA olymerase a/primase. It negatively regulates CDK2 activities and suppressesDNAreplication. Therefore, identification of other p12DOC-1=CDK2AP1 interacting proteins might clarify its role in the cell cycle regulation and carcinogenesis. The purpose of this study was to identify additional p12DOC-1=CDK2AP1 interacting proteins using the yeast two-hybrid system. Using human p12DOC-1=CDK2AP1 as a bait in a liver cDNA library screening, cDNA clones identical to human DOC-1R transcript were identified. The interaction between p12DOC-1=CDK2AP1 and p14DOC-1R was verified in vitro and in cells. GST pull-down assay and immunoprecipitation experiments confirmed the interaction between the two proteins. The ritical region for p12DOC-1=CDK2AP1's interaction with p14DOC-1R was defined to amino acids 20-25 by using a series of deletion mutants as baits in the yeast two-hybrid system. Our data indicated that p12DOC-1=CDK2AP1 could associate with its homologous protein, p14DOC-1R.