TI  - <prot>Hepatitis B virus X protein</prot> is a transcriptional modulator that
      communicates with <prot>transcription factor IIB</prot> and the <prot>RNA polymerase II
      subunit 5</prot>.
PG  - 7132-9
AB  - <prot>Hepatitis B virus X protei</prot>n (<prot>HBx</prot>) transactivates viral and cellular genes
      through a wide variety of cis-elements. However, the mechanism is still
      obscure. Our finding that  <prot>HBx</prot>  directly interacts with  <prot>RNA polymerase II
      subunit 5</prot> (<prot>RPB5</prot>) , a common subunit of RNA polymerases, implies that <prot>HBx</prot>
      directly modulates the function of RNA polymerase (Cheong, J. H., Yi, M.,
      Lin, Y., and Murakami, S. (1995) EMBO J. 14, 142-150). In this context, we
      examined the possibility that <prot>HBx</prot> and <prot>RPB5</prot> interact with other general
      transcription factors.  <prot>HBx</prot>  and  <prot>RPB5</prot>  specifically bound to  <prot>transcription
      factor IIB</prot> (<prot>TFIIB</prot>)  in vitro, both of which were detected by either
      far-Western blotting or the glutathione S-transferase-resin pull-down
      assay. Delineation of the binding regions of these three proteins revealed
      that  <prot>HBx</prot> ,  <prot>RPB5</prot> , and  <prot>TFIIB</prot>  each has two binding regions for the other two
      proteins. Co-immunoprecipitation using HepG2 cell lysates that express <prot>HBx</prot>
      demonstrated trimeric interaction in vivo. Some <prot>HBx</prot> substitution mutants,
      which had severely impaired transacting activity, exhibited reduced
      binding affinity with either <prot>TFIIB</prot> or <prot>RPB5</prot> in a mutually exclusive manner,
      suggesting that  <prot>HBx</prot>  transactivation requires the interactions of both  <prot>RPB5</prot> 
      and  <prot>TFIIB</prot> . These results indicated that <prot>HBx</prot> is a novel virus modulator
      that facilitates transcriptional initiation by stabilizing the association
      between RNA polymerase and <prot>TFIIB</prot> through communication with <prot>RPB5</prot> and
      <prot>TFIIB</prot>.
AD  - Department of Molecular Biology, Cancer Research Institute, Kanazawa
