Journal of Virology, November 2001, p. 10779-10786, Vol. 75, No. 22
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.22.10779-10786.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Pathology, VA Medical Center 113B, University of California School of Medicine, San Francisco, California 94121,1 and Department of Molecular Microbiology and Immunology, Howard Hughes Medical Institute, Keck School of Medicine, University of Southern California, Los Angeles, California 900332
Received 18 April 2001/Accepted 7 August 2001
The hepatitis B virus posttranscriptional regulatory element (PRE) is an RNA element that increases the expression of unspliced mRNAs, apparently by facilitating their export from the nucleus. We have identified a cellular protein that binds to the PRE as the polypyrimidine tract binding protein (PTB), which shuttles rapidly between the nucleus and the cytoplasm. Mutants of the PRE with mutations in PTB binding sites show markedly decreased activity, while cells that stably overexpress PTB show increased PRE-dependent gene expression. Export of PTB from the nucleus, like PRE function, is blocked by a mutant form of Ran binding protein 1 but not by leptomycin B. Therefore, PTB is important for PRE activity and appears to function as an export factor for PRE-containing mRNAs.
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