The 3' untranslated region complex involved in stabilization of human alpha-globin mRNA assembles in the nucleus and serves an independent role as a splice enhancer.
Posttranscriptional controls, mediated primarily by RNA-protein complexes, have the potential to alter multiple steps in RNA processing and function. Human alpha-globin mRNA is bound at a C-rich motif in the 3' untranslated region (3'UTR) by the KH domain protein alpha-globin poly(C)-binding protein (alphaCP). This "alpha-complex" is essential to cytoplasmic stability of alpha-globin mRNA in erythroid cells. Here we report that the 3'UTR alpha-complex also serves an independent nuclear role as a splice enhancer. Consistent with this role, we find that alphaCP binds alpha-globin transcripts prior to splicing. Surprisingly, this binding occurs at C-rich sites within intron I as well as at the 3'UTR C-rich determinant. The intronic and 3'UTR alphaCP complexes appear to have distinct effects on splicing. While intron I complexes repress intron I excision, the 3'UTR complex enhances splicing of the full-length transcript both in vivo and in vitro. In addition to its importance to splicing, nuclear assembly of the 3'UTR alphaCP complex may serve to "prepackage" alpha-globin mRNA with its stabilizing complex prior to cytoplasmic export. Linking nuclear and cytoplasmic controls by the action of a particular RNA-binding protein, as reported here, may represent a modality of general importance in eukaryotic gene regulation.
Ji
Xinjun
X
Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Kong
Jian
J
Carstens
Russ P
RP
Liebhaber
Stephen A
SA
D020413:3' Untranslated Regions / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics*; D005914:Globins / Q000235:genetics*; D006801:Humans; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D011485:Protein Binding; D012326:RNA Splicing / Q000235:genetics*; D020871:RNA Stability / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000378:metabolism; D038621:Regulatory Sequences, Ribonucleic Acid / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics
D020413:3' Untranslated Regions; C501903:PCBP2 protein, human; D016601:RNA-Binding Proteins; D038621:Regulatory Sequences, Ribonucleic Acid; D005914:Globins