Identification of a motif that mediates polypyrimidine tract-binding protein-dependent internal ribosome entry.
We have identified a novel motif which consists of the sequence (CCU)(n) as part of a polypyrimidine-rich tract and permits internal ribosome entry. A number of constructs containing variations of this motif were generated and these were found to function as artificial internal ribosome entry segments (AIRESs) in vivo and in vitro in the presence of polypyrimidine tract-binding protein (PTB). The data show that for these sequences to function as IRESs the RNA must be present as a double-stranded stem and, in agreement with this, rather surprisingly, we show that PTB binds strongly to double-stranded RNA. All the cellular 5' untranslated regions (UTRs) tested that harbor this sequence were shown to contain internal ribosome entry segments that are dependent upon PTB for function in vivo and in vitro. This therefore raises the possibility that PTB or its interacting protein partners could provide a bridge between the IRES-RNA and the ribosome. Given the number of putative cellular IRESs that could be dependent on PTB for function, these data strongly suggest that PTB-1 is a universal IRES-trans-acting factor.
Mitchell
Sally A
SA
School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
Spriggs
Keith A
KA
Bushell
Martin
M
Evans
Joanne R
JR
Stoneley
Mark
M
Le Quesne
John P C
JP
Spriggs
Ruth V
RV
Willis
Anne E
AE
D020121:5' Untranslated Regions; D001483:Base Sequence; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D038941:Polypyrimidine Tract-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D012270:Ribosomes; D012689:Sequence Homology, Nucleic Acid
D020121:5' Untranslated Regions; D012333:RNA, Messenger; D038941:Polypyrimidine Tract-Binding Protein