Objective    To explore the interaction between hepatitis B virus PreS1 protein and nascent-polypeptide-associated complex alpha polypeptide (NACA).      Methods    Mating experiment and in vitro binding assays were carried out to verify the interaction between hepatitis B virus PreS1 protein and NACA in vivo and in vitro respectively in yeast cells. Coimmunoprecipitation was employed to demonstrate the binding reaction between the 2 proteins in mammalian cells.     Results    In mating experiment

the resulting diploids containing pAS2-preS1 and pACT2-NACA plasmids turned to blue in the

X-gal assay. Western blot analysis displayed a positive reactive strap

which indicating PreS1 protein interacted directly with NACA in vitro binding assays. Moreover

interaction between the 2 proteins in mammalian cells was confirmed by coimmunoprecipitation

with a protein strap about 13×10

3

in Western blot.     Conclusion    Specific interaction exists between hepatitis B virus PreS1 protein and NACA in both prokaryotic and mammalian cells. NACA protein probably takes part in the adhesion and transactivation of HBV through the binding with PreS1.