The hepatitis B pX protein promotes dimerization and DNA binding of cellular basic region/leucine zipper proteins by targeting the conserved basic region

UMMS Affiliation

Howard Hughes Medical Institute, Program in Molecular Medicine

Publication Date


Document Type



Amino Acid Sequence; Conserved Sequence; DNA; Dimerization; Gene Products, tax; Hepatitis B Antigens; Humans; *Leucine Zippers; Molecular Sequence Data; Protein Kinases; Retroviridae Proteins, Oncogenic; Trans-Activation (Genetics); Trans-Activators; *Transcription Factors; Viral Envelope Proteins; Viral Regulatory and Accessory Proteins


Life Sciences | Medicine and Health Sciences


The hepatitis B virus pX protein is a potent transcriptional activator of viral and cellular genes whose mechanism of action is poorly understood. Here we show that pX dramatically stimulates in vitro DNA binding of a variety of cellular proteins that contain basic region/leucine zipper (bZIP) DNA binding domains. The basis for increased DNA binding is a direct interaction between pX and the conserved bZIP basic region, which promotes bZIP dimerization and the increased concentration of the bZIP homodimer then drives the DNA binding reaction. Unexpectedly, we found that the DNA binding specificity of various pX-bZIP complexes differs from one another and from that of the bZIP itself. Thus, through recognition of the conserved basic region, pX promotes dimerization, increases DNA binding, and alters DNA recognition. These properties of pX are remarkably similar to those of the human T-cell lymphotrophic virus type I Tax protein. Although Tax and pX are not homologous, we show that the regions of the two proteins that stimulate bZIP binding contain apparent metal binding sites. Finally, consistent with this in vitro activity, we provide evidence that both Tax and pX activate transcription in vivo, at least in part, by facilitating occupancy of bZIPs on target promoters.

DOI of Published Version



J Biol Chem. 1999 May 14;274(20):13970-7.

Journal/Book/Conference Title

The Journal of biological chemistry

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Link to Article in PubMed

PubMed ID