Biochemistry and functions of hepatitis B virus X protein

Intervirology. 1995;38(1-2):89-99. doi: 10.1159/000150417.


Hepatitis B virus X gene codes for a small basic cytoplasmic protein and is able to transactivate viral and cellular genes, although X protein exhibits no DNA-binding activity. The mechanism of transactivation by X protein has been suggested to be via protein-protein interaction(s). X protein had amino acid sequences homologous to the functionally essential domain of Kunitz-type serine protease inhibitors, and these sequences were indispensable for transactivation function. X protein activated X-gene transcription itself and an X-responsive element were localized in their minimal promoter. Furthermore, tumor suppressor gene product p53, but not mutant p53, repressed X-gene transcription from the minimal promoter, indicating that X protein disrupts the function of normal p53, which represses transcription of X gene or cellular gene. Data suggest that inhibition of a hepatic serine protease by X protein leads to eliminate the suppressor effect of p53 on the basic transcription machinery in nucleus.

Publication types

  • Review

MeSH terms

  • Amino Acid Sequence
  • Gene Expression Regulation, Viral
  • Genes, p53
  • Hepatitis B virus / chemistry
  • Hepatitis B virus / genetics
  • Molecular Sequence Data
  • Mutation
  • Promoter Regions, Genetic
  • Serine Proteinase Inhibitors / chemistry
  • Serine Proteinase Inhibitors / physiology
  • Trans-Activators* / chemistry
  • Trans-Activators* / genetics
  • Trans-Activators* / physiology*
  • Transcription, Genetic


  • Serine Proteinase Inhibitors
  • Trans-Activators
  • hepatitis B virus X protein