Aim:To explore the different roles of pancreatic duodenal homeobox factors-1(PDX-1)domains in PDX-1 mediated repression of human cytomegalovirus imme-diately early(CMV IE)promoter.Methods:A series of truncated PDX-1 mutantswere constructed.The binding of PDX-1 and CMV IE promoter was identified byelectrophoretic mobility shift assay(EMSA).The dual-reporter assay was ap-plied to examine the repression activities of PDX-1 mutants on CMV IE promoter.In addition,RNAi technology was used to specifically knock down the endog-enous PDX-1 expression.Results:The reporter assay indicated that compared tothe mock controls(pEGFP-N2),overexpression of PDX-1 resulted in a 41% de-crease of CMV IE promoter activity in the 293 cells(P<0.05)and 43% decrease inHeLa cells(P<0.05),and the repression levels of various truncated mutants playedon CMV IE promoter were different.Specific knock down of the endogenousPDX-1 expression significantly restored the activity of CMV IE promoter.EMSAdemonstrated that domain 3 is necessary for nuclear localization and DNA bind-ing activity of PDX-1.However,binding of PDX-1 alone to CMV IE promoter wasnot sufficient to inhibit its transcriptional activity,and other domains of PDX-1presented were also required.Conclusion:Our data suggested that the DNAbinding activity of PDX-1 domain 3 and the cooperative binding of PDX-1 domain1/2 with other proteins were required for PDX-1 mediated repression of CMV IEpromoter. Aim: To explore the different roles of pancreatic duodenal homeobox factors-1 (PDX-1) domains in PDX-1 mediated repression of human cytomegalovirus imme-diately early (CMV IE) promoter. Methods. A series of truncated PDX-1 mutantswere constructed . The binding of PDX-1 and CMV IE promoter was identified by electrophoretic mobility shift assay (EMSA). The dual-reporter assay was ap-plied to examine the repression activities of PDX-1 mutants on CMV IE promoter. was used to specifically knock down the endog-enous PDX-1 expression. Results: The reporter assay indicated that compared to tCE mock controls (pEGFP-N2), overexpression of PDX-1 resulted in 41% de- crease of CMV IE promoter activity in the 293 cells (P <0.05) and 43% decrease in HeLa cells (P <0.05), and the repression levels of various truncated mutants played on CMV IE promoter were different. Specifically knock down of the endogenous PDX-1 expression was significantly restored the activity of CMV IE promoter.EMSAdemonstrated that dom ain 3 is necessary for nuclear localization and DNA bind-ing activity of PDX-1.However, binding of PDX-1 alone to CMV IE promoter wasnot sufficient to inhibit its transcriptional activity, and other domains of PDX-1 represented also also required. Conlusion : Our data suggested that the DNA binding activity of PDX-1 domain 3 and the cooperative binding of PDX-1 domain1 / 2 with other proteins were required for PDX-1 mediated repression of CMV IE promoter.