A novel splicing regulator shares a nuclear import pathway with SR proteins.
Alternative splicing of precursor mRNA is often regulated by serine/arginine-rich proteins (SR proteins) and hnRNPs, and varying their concentration in the nucleus can be a mechanism for controlling splice site selection. To understand the nucleocytoplasmic transport mechanism of splicing regulators is of key importance. SR proteins are delivered to the nucleus by transportin-SRs (TRN-SRs), importin beta-like nuclear transporters. Here we identify and characterize a non-SR protein, RNA-binding motif protein 4 (RBM4), as a novel substrate of TRN-SR2. TRN-SR2 interacts specifically with RBM4 in a Ran-sensitive manner. TRN-SR2 indeed mediates the nuclear import of a recombinant protein containing the RBM4 C-terminal domain. This domain serves as a signal for both nuclear import and export, and for nuclear speckle targeting. Finally, both in vivo and in vitro splicing analyses demonstrate that RBM4 not only modulates alternative pre-mRNA splicing but also acts antagonistically to authentic SR proteins in splice site and exon selection. Thus, a novel splicing regulator with opposite activities to SR proteins shares an identical import pathway with SR proteins to the nucleus.
Lai
Ming-Chih
MC
Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
Kuo
Hao-Wei
HW
Chang
Wen-Cheng
WC
Tarn
Woan-Yuh
WY
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001221:Aspartate Carbamoyltransferase / Q000378:metabolism; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D004080:Dihydroorotase / Q000378:metabolism; D005091:Exons; D017344:Genes, Insect; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009414:Nerve Growth Factors; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism; D022821:RNA Splice Sites; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D020798:Two-Hybrid System Techniques; D028961:beta Karyopherins / Q000378:metabolism
C033626:CAD trifunctional enzyme; C099695:MANF protein, human; D009097:Multienzyme Complexes; D009414:Nerve Growth Factors; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; C473692:RBM4 protein, human; D012322:RNA Precursors; D022821:RNA Splice Sites; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D028961:beta Karyopherins; C424165:transportin SR2; D012694:Serine; D001221:Aspartate Carbamoyltransferase; D004080:Dihydroorotase; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)