Polypyrimidine tract binding protein blocks the 5' splice site-dependent assembly of U2AF and the prespliceosomal E complex.
Polypyrimidine tract binding protein (PTB) represses some alternatively spliced exons by direct occlusion of splice sites. In repressing the splicing of the c-src N1 exon, we find that PTB acts by a different mechanism. PTB does not interfere with U1 snRNP binding to the N1 5' splice site. Instead, PTB prevents formation of the prespliceosomal early (E) complex across the intervening intron by preventing the assembly of the splicing factor U2AF on the 3' splice site of exon 4. When the unregulated 5' splice site of the upstream exon 3 is present, U2AF binding is restored and splicing between exons 3 and 4 proceeds in spite of the N1 exon bound PTB. Thus, rather than directly blocking the N1 splice sites, PTB prevents the 5' splice site-dependent assembly of U2AF into the E complex. This mechanism likely occurs in many other alternative exons.
Sharma
Shalini
S
Howard Hughes Medical Institute, University of California, Los Angeles, MRL5-748, Charles E. Young Drive South, Los Angeles, California 90095, USA.
Falick
Arnold M
AM
Black
Douglas L
DL
D020121:5' Untranslated Regions / Q000378:metabolism*; D017398:Alternative Splicing; D001483:Base Sequence; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D007438:Introns; D046911:Macromolecular Substances / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D038941:Polypyrimidine Tract-Binding Protein / Q000502:physiology*; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism*; D000072668:Splicing Factor U2AF
D020121:5' Untranslated Regions; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; D012261:Ribonucleoproteins; D000072668:Splicing Factor U2AF; C000607494:U2AF2 protein, human; D038941:Polypyrimidine Tract-Binding Protein