Objective    To further investigate the function of chromatin insulators and to construct a screen system for chromatin insulators.     Methods    A primer set targeting chicken cHS4 locus was designed and synthesized. The specific PCR product using this primer set was obtained and sequenced. In order to test its blocking activity

we further inserted this fragment between enhancer and promotor. Then TK gene was inserted into modified pEGFP-N1 plasmid

which was tested for its negative and positive selection.     Results    The result of  luciferase activity showed that insulators could function when it was located on plasmid. Then vector pEGFP-N1 was modified as a screening system for chromatin insulator

in which phosphotransferase gene and thymidine kinase gene could function as selection marker. In order to evaluate its efficiency and viability

the recombinant vector was transfected into COS-7 cells. After selected with G418 for 10 d

stable transfected cells with G418 resistance were obtained. The sensitivity to pro-drug of GCV of these cells was different from that of its control cells by MTT.     Conclusion    This study provides an early research to further screen and utilize chromatin insulator in eukaryotes.