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Molecular and Cellular Biology, December 1998, p. 7546-7555, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

RMP, a Novel RNA Polymerase II Subunit 5-Interacting Protein, Counteracts Transactivation by Hepatitis B Virus X Protein

Dorjbal Dorjsuren, Yong Lin, Wenxiang Wei, Tatsuya Yamashita, Takahiro Nomura, Naoyuki Hayashi, and Seishi Murakami*

Department of Molecular Oncology, Cancer Research Institute, Kanazawa University, Kanazawa 920-0934, Japan

Received 11 May 1998/Returned for modification 22 June 1998/Accepted 2 September 1998

To modulate transcription, regulatory factors communicate with basal transcription factors and/or RNA polymerases in a variety of ways. Previously, it has been reported that RNA polymerase II subunit 5 (RPB5) is one of the targets of hepatitis B virus X protein (HBx) and that both HBx and RPB5 specifically interact with general transcription factor IIB (TFIIB), implying that RPB5 is one of the communicating subunits of RNA polymerase II involved in transcriptional regulation. In this context, we screened for a host protein(s) that interacts with RPB5. By far-Western blot screening, we cloned a novel gene encoding a 508-amino-acid-residue RPB5-binding protein from a HepG2 cDNA library and designated it RPB5-mediating protein (RMP). Expression of RMP mRNA was detected ubiquitously in various tissues. Bacterially expressed recombinant RMP strongly bound RPB5 but neither HBx nor TATA-binding protein in vitro. Endogenous RMP was immunologically detected interacting with assembled RPB5 in RNA polymerase in mammalian cells. The central part of RMP is responsible for RPB5 binding, and the RMP-binding region covers both the TFIIB- and HBx-binding sites of RPB5. Overexpression of RMP, but not mutant RMP lacking the RPB5-binding region, inhibited HBx transactivation of reporters with different HBx-responsive cis elements in transiently transfected cells. The repression by RMP was counteracted by HBx in a dose-dependent manner. Furthermore, RMP has an inhibitory effect on transcriptional activation by VP16 in the absence of HBx. These results suggest that RMP negatively modulates RNA polymerase II function by binding to RPB5 and that HBx counteracts the negative role of RMP on transcription indirectly by interacting with RPB5.

* Corresponding author. Mailing address: Department of Molecular Oncology, Cancer Research Institute, Kanazawa University, Takara-machi 13-1, Kanazawa 920-0934. Japan. Phone: 81-76-265-2731. Fax: 81-76-234-4501. E-mail: semuraka{at}kenroku.kanazawa-u.ac.jp.

Molecular and Cellular Biology, December 1998, p. 7546-7555, Vol. 18, No. 12
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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