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.
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 5' 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.
Hellen
C U
CU
Department of Microbiology, State University of New York, Stony Brook 11794-8621.
Witherell
G W
GW
Schmid
M
M
Shin
S H
SH
Pestova
T V
TV
Gil
A
A
Wimmer
E
E
D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004686:Encephalomyocarditis virus / Q000235:genetics / Q000378:metabolism*; D005914:Globins / Q000096:biosynthesis; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000302:isolation & purification / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D017955:Poliovirus / Q000235:genetics / Q000378:metabolism*; D038941:Polypyrimidine Tract-Binding Protein; D014176:Protein Biosynthesis; D012322:RNA Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012367:RNA, Viral / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015183:Restriction Mapping; D012270:Ribosomes / Q000378:metabolism*
D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins; D012322:RNA Precursors; D012333:RNA, Messenger; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D038941:Polypyrimidine Tract-Binding Protein; D005914:Globins