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Role of polypyrimidine tract binding protein in the function of the hepatitis B virus posttranscriptional regulatory element.

ABSTRACT: 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.

SUBMITTER: Zang WQ

PROVIDER: S-EPMC114659 | biostudies-literature | 2001 Nov

REPOSITORIES: biostudies-literature

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Role of polypyrimidine tract binding protein in the function of the hepatitis B virus posttranscriptional regulatory element.

Zang W Q WQ Li B B Huang P Y PY Lai M M MM Yen T S TS

Journal of virology 20011101 22

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 ...[more]

PMID: 11602719

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Project description:BACKGROUND: Earlier we have reported translational control of interferon regulatory factor 2 (IRF2) by internal initiation (Dhar et al, Nucleic Acids Res, 2007). The results implied possible role of IRF2 in controlling the intricate balance of cellular gene expression under stress conditions in general. Here we have investigated the secondary structure of the Internal Ribosome Entry Site of IRF2 RNA and demonstrated the role of PTB protein in ribosome assembly to facilitate internal initiation. METHODOLOGY/PRINCIPAL FINDINGS: We have probed the putative secondary structure of the IRF2 5'UTR RNA using various enzymatic and chemical modification agents to constrain the secondary structure predicted from RNA folding algorithm Mfold. The IRES activity was found to be influenced by the interaction of trans-acting factor, polypyrimidine tract binding protein (PTB). Deletion of 25 nts from the 3'terminus of the 5'untranslated region resulted in reduced binding with PTB protein and also showed significant decrease in IRES activity compared to the wild type. We have also demonstrated putative contact points of PTB on the IRF2-5'UTR using primer extension inhibition assay. Majority of the PTB toe-prints were found to be restricted to the 3'end of the IRES. Additionally, Circular Dichroism (CD) spectra analysis suggested change in the conformation of the RNA upon PTB binding. Further, binding studies using S10 extract from HeLa cells, partially silenced for PTB gene expression, resulted in reduced binding by other trans-acting factors. Finally, we have demonstrated that addition of recombinant PTB enhances ribosome assembly on IRF2 IRES suggesting possible role of PTB in mediating internal initiation of translation of IRF2 RNA. CONCLUSION/SIGNIFICANCE: It appears that PTB binding to multiple sites within IRF2 5'UTR leads to a conformational change in the RNA that facilitate binding of other trans-acting factors to mediate internal initiation of translation.

Dataset Information

Role of polypyrimidine tract binding protein in the function of the hepatitis B virus posttranscriptional regulatory element.

Publications

Role of polypyrimidine tract binding protein in the function of the hepatitis B virus posttranscriptional regulatory element.

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