Dimerization of hepatitis B viral X protein synthesized in a cell-free system

Hepatitis B viral X protein (HBx), a 17-kDa polypeptide, has been demonstrated as a trans-acting factor. In this study, we report that the HBx was able to form a dimer, a feature very similar to many well known trans-acting factors. In vitro synthesized HBx, after immunoprecipitation and analysis by SDS-PAGE, appeared as one prominent 17-kDa band (monomer) and a faint 34-kDa band (dimer). The amount of dimer increased if the sample of immunoprecipitated HBx was not treated with 2-mecaptoethanol, indicating the dimer was held together by the disulfide linkage. Dimerization of a truncated HBx established that the four cysteine residues close to the N-terminus are sufficient for the dimerization process.