A cytoplasmic 57-kDa protein that is required for translation of picornavirus RNA by internal ribosomal entry is identical to the nuclear pyrimidine tract-binding protein.
- 15 August 1993
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 90 (16), 7642-7646
- https://doi.org/10.1073/pnas.90.16.7642
Abstract
Initiation of translation of the RNA genomes of picornaviruses such as poliovirus and encephalomyocarditis virus is cap-independent and results from interaction of ribosomes with a segment of the 59 noncoding region of these mRNAs termed the internal ribosomal entry site. Genetic and biochemical studies have previously shown that a 57-kDa cytoplasmic RNA-binding protein (p57) plays an essential role in this translation mechanism. We have now found that p57 shares physical, biochemical, and antigenic properties with the pyrimidine tract-binding protein (PTB), a nuclear protein that has been implicated in various processes involving pre-mRNA. These data indicate that p57 and PTB are the same protein. Purified recombinant PTB bound specifically to a bulged hairpin within the internal ribosomal entry site of encephalomyocarditis virus and had a much lower affinity for a mutated derivative of this hairpin and for unrelated RNAs. Immunodepletion of p57/PTB from a HeLa cell-free lysate inhibited translation of poliovirus and encephalomyocarditis virus mRNAs but had no effect on translation of beta-globin mRNA, confirming the essential role of p57 in translation by internal ribosomal entry.Keywords
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