Examples of associations between human disease and defects in pre–messenger RNA splicing/alternative splicing are accumulating. Although many alterations are caused by mutations in splicing signals or regulatory sequence elements, recent... more
Examples of associations between human disease and defects in pre–messenger RNA splicing/alternative splicing are accumulating. Although many alterations are caused by mutations in splicing signals or regulatory sequence elements, recent studies have noted the disruptive impact of mutated generic spliceosome components and splicing regulatory proteins. This review highlights recent progress in our understanding of how the altered splicing function of RNA-binding proteins contributes to myelodysplastic syndromes, cancer, and neuropathologies.
Research Interests:
Medicinal chemistry optimization of a previously described stilbene inhibitor of HIV-1, 5350150 (2-(2-(5-nitro-2-thienyl)vinyl)quinoline), led to the identification of the thiazole-5-carboxamide derivative (GPS491), which retained potent... more
Medicinal chemistry optimization of a previously described stilbene inhibitor of HIV-1, 5350150 (2-(2-(5-nitro-2-thienyl)vinyl)quinoline), led to the identification of the thiazole-5-carboxamide derivative (GPS491), which retained potent anti-HIV-1 activity with reduced toxicity. In this report, we demonstrate that the block of HIV-1 replication by GPS491 is accompanied by a drastic inhibition of viral gene expression (IC50 ~ 0.25 µM), and alterations in the production of unspliced, singly spliced, and multiply spliced HIV-1 RNAs. GPS491 also inhibited the replication of adenovirus and multiple coronaviruses. Low µM doses of GPS491 reduced adenovirus infectious yield ~1000 fold, altered virus early gene expression/viral E1A RNA processing, blocked viral DNA amplification, and inhibited late (hexon) gene expression. Loss of replication of multiple coronaviruses (229E, OC43, SARS-CoV2) upon GPS491 addition was associated with the inhibition of viral structural protein expression and t...
Research Interests:
Aberrant expression of Protein Arginine Methyltransferases (PRMTs) has been observed in several cancer types, including breast cancer. We previously reported that the PRMT1v2 isoform, which is generated through inclusion of alternative... more
Aberrant expression of Protein Arginine Methyltransferases (PRMTs) has been observed in several cancer types, including breast cancer. We previously reported that the PRMT1v2 isoform, which is generated through inclusion of alternative exon 2, is overexpressed in breast cancer cells and promotes their invasiveness. However, the precise mechanism by which expression of this isoform is controlled and how it is dysregulated in breast cancer remains unknown. Using a custom RNA interference-based screen, we identified several RNA binding proteins (RBP) which, when knocked down, altered the relative abundance of the alternatively spliced PRMT1v2 isoform. Amongst the top hits were SNW Domain containing 1 (SNW1) and RBP-associated with lethal yellow mutation (RALY), which both associated with the PRMT1 pre-mRNA and upon depletion caused an increase or decrease in the relative abundance of PRMT1v2 isoform mRNA and protein. Most importantly, a significant decrease in invasion was observed upo...
Research Interests:
A 256-compound library was evaluated in an anti-HIV screen to identify structural "mimics" of the fused tetracyclic indole compound 1 (IDC16) that conserve its anti-HIV activity without associated cytotoxicity. Four... more
A 256-compound library was evaluated in an anti-HIV screen to identify structural "mimics" of the fused tetracyclic indole compound 1 (IDC16) that conserve its anti-HIV activity without associated cytotoxicity. Four diheteroarylamide-type compounds, containing a common 5-nitroisobenzothiazole motif, were identified as active. In subsequent screens, the most potent compound 9 (1C8) was active against wild-type HIV-1IIIB (subtype B, X4-tropic), and HIV-1 97USSN54 (subtype A, R5-tropic) with EC50's of 0.6 and 0.9 μM, respectively. Compound 9 also inhibited HIV strains resistant to drugs targeting HIV reverse transcriptase, protease, integrase, and coreceptor CCR5 with EC50's ranging from 0.9-1.50 μM. The CC50 value obtained in a cytotoxicity assay for compound 9 was > 100 μM, corresponding to a therapeutic index (CC50/EC50) of approximately 100. Further comparison studies revealed that, whereas the anti-HIV activity for compound 9 and the parent molecule 1 are simi...
Research Interests:
Myotonic dystrophy type 1 (DM1) is a neuromuscular disorder caused by an expansion of CUG repeats in the 3' UTR of the DMPK gene. The CUG repeats form aggregates of mutant mRNA, which cause misregulation and/or sequestration of... more
Myotonic dystrophy type 1 (DM1) is a neuromuscular disorder caused by an expansion of CUG repeats in the 3' UTR of the DMPK gene. The CUG repeats form aggregates of mutant mRNA, which cause misregulation and/or sequestration of RNA-binding proteins, causing aberrant alternative splicing in cells. Previously, we showed that the multi-functional RNA-binding protein Staufen1 (Stau1) was increased in skeletal muscle of DM1 mouse models and patients. We also showed that Stau1 rescues the alternative splicing profile of pre-mRNAs, e.g. the INSR and CLC1, known to be aberrantly spliced in DM1. In order to explore further the potential of Stau1 as a therapeutic target for DM1, we first investigated the mechanism by which Stau1 regulates pre-mRNA alternative splicing. We report here that Stau1 regulates the alternative splicing of exon 11 of the human INSR via binding to Alu elements located in intron 10. Additionally, using a high-throughput RT-PCR screen, we have identified numerous Stau1-regulated alternative splicing events in both WT and DM1 myoblasts. A number of these aberrant ASEs in DM1, including INSR exon 11, are rescued by overexpression of Stau1. However, we find other ASEs in DM1 cells, where overexpression of Stau1 shifts the splicing patterns away from WT conditions. Moreover, we uncovered that Stau1-regulated ASEs harbour Alu elements in intronic regions flanking the alternative exon more than non-Stau1 targets. Taken together, these data highlight the broad impact of Stau1 as a splicing regulator and suggest that Stau1 may act as a disease modifier in DM1.
Research Interests:
Research Interests:
The heterogeneous nuclear ribonucleoprotein (hnRNP) family includes a diverse group of RNA binding proteins to which we are affiliating here other structurally and functionally related proteins (e.g., Nova, Sam68, ESRP, Fox, TDP‑43, Hu,... more
The heterogeneous nuclear ribonucleoprotein (hnRNP) family includes a diverse group of RNA binding proteins to which we are affiliating here other structurally and functionally related proteins (e.g., Nova, Sam68, ESRP, Fox, TDP‑43, Hu, CUG‑BP, MBNL and TIA proteins). These hnRNP and hnRNP‑like proteins make important contributions to protein diversity and activity by modulating the alternative splicing of a large repertoire of pre‑mRNAs. They achieve this function through a variety of molecular strategies ranging from directly preventing the recognition of splice sites, antagonizing or helping the assembly of positive regulatory complexes, interfering with spliceosome assembly and changing the conformation of pre‑mRNAs. In addition to regulating key splicing events, defects in the expression of these proteins are now being documented for a growing number of human diseases including cancer. hnRNP and hnRNP‑like proteins therefore represent a group of proteins whose roles in the cont...
The poly(A)-binding protein nuclear 1 is encoded by the PABPN1 gene, whose mutations result in oculopharyngeal muscular dystrophy, a late-onset disorder for which the molecular basis remains unknown. Despite recent studies investigating... more
The poly(A)-binding protein nuclear 1 is encoded by the PABPN1 gene, whose mutations result in oculopharyngeal muscular dystrophy, a late-onset disorder for which the molecular basis remains unknown. Despite recent studies investigating the functional roles of PABPN1, little is known about its regulation. Here, we show that PABPN1 negatively controls its own expression to maintain homeostatic levels in human cells. Transcription from the PABPN1 gene results in the accumulation of two major isoforms: an unspliced nuclear transcript that retains the 3'-terminal intron and a fully spliced cytoplasmic mRNA. Increased dosage of PABPN1 protein causes a significant decrease in the spliced/unspliced ratio, reducing the levels of endogenous PABPN1 protein. We also show that PABPN1 autoregulation requires inefficient splicing of its 3'-terminal intron. Our data suggest that autoregulation occurs via the binding of PABPN1 to an adenosine (A)-rich region in its 3' untranslated region, which promotes retention of the 3'-terminal intron and clearance of intron-retained pre-mRNAs by the nuclear exosome. Our findings unveil a mechanism of regulated intron retention coupled to nuclear pre-mRNA decay that functions in the homeostatic control of PABPN1 expression.
Research Interests:
Modification of splicing by chemotherapeutic drugs has usually been evaluated on a limited number of pre-mRNAs selected for their recognized or potential importance in cell proliferation or apoptosis. However, the pathways linking... more
Modification of splicing by chemotherapeutic drugs has usually been evaluated on a limited number of pre-mRNAs selected for their recognized or potential importance in cell proliferation or apoptosis. However, the pathways linking splicing alterations to the efficiency of cancer therapy remain unclear. Next-generation sequencing was used to analyse the transcriptome of breast carcinoma cells treated by cisplatin. Pharmacological inhibitors, RNA interference, cells deficient in specific signalling pathways, RT-PCR and FACS analysis were used to investigate how the anti-cancer drug cisplatin affected alternative splicing and the cell death pathway. We identified 717 splicing events affected by cisplatin, including 245 events involving cassette exons. Gene ontology analysis indicates that cell cycle, mRNA processing and pre-mRNA splicing were the main pathways affected. Importantly, the cisplatin-induced splicing alterations required class I PI3Ks P110β but not components such as ATM, ...
Research Interests:
A large number of novel cellular proto-oncogenes have been identified and cloned by analysis of common integration sites in retrovirally induced malignancies. In the multistage erythroleukemias induced by the various strains of Friend... more
A large number of novel cellular proto-oncogenes have been identified and cloned by analysis of common integration sites in retrovirally induced malignancies. In the multistage erythroleukemias induced by the various strains of Friend leukemia virus, the analysis of proviral-integration events has led to the identification of two genes, Fli-1 and Spi-1, both novel members of the ets oncogene family of transcription factors. In this report, we describe the identification of another integration site, designated Fli-2 (Friend leukemia virus integration-2), in an erythroleukemia cell line induced by Friend murine leukemia virus (F-MuLV). Rearrangements at the Fli-2 locus were found in two erythroleukemia cell lines independently induced by F-MuLV and one leukemic cell line derived from the spleen of a mouse infected with the polycythemia strain of Friend leukemia virus. The deduced amino acid sequence of a cDNA corresponding to a transcript originating from genomic DNA adjacent to Fli-2...
Research Interests:
The diagnosis and consequently the treatment of post-psychotic depression are essential since depression in schizophrenia has often been associated with suicide (Siris, 2001). The role of antidepressants in this common clinical situation... more
The diagnosis and consequently the treatment of post-psychotic depression are essential since depression in schizophrenia has often been associated with suicide (Siris, 2001). The role of antidepressants in this common clinical situation is unclear (Addington et al., 2002). Thus ...
Research Interests:
Max is a member of the b-HLH-LZ (basic region-helix1-loop-helix2-leucine zipper) family of eukaryotic transcription factors. It is the obligate partner of the related b-HLH-LZ proteins, c-Myc and Mad1, with which it forms heterodimers on... more
Max is a member of the b-HLH-LZ (basic region-helix1-loop-helix2-leucine zipper) family of eukaryotic transcription factors. It is the obligate partner of the related b-HLH-LZ proteins, c-Myc and Mad1, with which it forms heterodimers on target DNA. While c-Myc and Mad1 require Max for DNA-binding, Max itself can form a homodimer that recognizes E-box DNA sequences (CACGTG) in gene promoters that are targeted by c-Myc. Evidence suggests that this mode of binding by Max may repress c-Myc transcriptional activity, and this may have applications in the control of the aberrant activity of c-Myc during certain oncogenic transformations. To enhance this repressive potential of Max, we sought to stabilize Max homodimers. We have designed a double mutant (N78V/H81L) located in the coiled-coil interface of the leucine zipper domain and we demonstrate that these mutations do indeed increase the stability of the protein. The mutations also improve the stability of the complex with cognate DNA. Thermal denaturations monitored by circular dichroism reveal two transitions that are due to intermediate folding states for both the wild-type and mutant proteins; this is supported by detailed thermodynamic analyses. A formalism to characterize the temperature-dependence of the unfolding, including the effect of intermediates, is presented.
Research Interests: Thermodynamics, Molecular Biology, Kinetics, Transcription Factors, Protein Engineering, and 20 moreDNA, Molecular, Humans, Mutation, Circular Dichroism, Polymerase Chain Reaction, Plasmids, Transcription Factor, Temperature Dependence, DNA binding, Genetic Recombination, Protein Conformation, Amino Acid Sequence, Thermodynamic Stability, Protein Denaturation, DNA binding proteins, Site-directed Mutagenesis, *Hot Temperature, Biochemistry and cell biology, and DNA sequence
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Page 77. Heterogeneous Nuclear Ribonucleoprotein Particle A/B Proteins and the Control of Alternative Splicing of the Mammalian Heterogeneous Nuclear Ribonucleoprotein Particle A1 Pre-mRNA B. Chabot, C. LeBel, S. Hutchison ...
Research Interests:
Research Interests:
With the functional importance of alternative splicing being validated in nearly every mammalian biological system and implicated in many human diseases, it is now crucial to identify the molecular programs that control the production of... more
With the functional importance of alternative splicing being validated in nearly every mammalian biological system and implicated in many human diseases, it is now crucial to identify the molecular programs that control the production of splice variants. In this article, I will survey how our knowledge of the basic principles of alternative splicing control evolved over the last 25 years. I will also describe how investigation of the splicing control of an apoptotic regulator led us to identify novel effectors and revealed the existence of converging pathways linking splicing decisions to DNA damage. Finally, I will review how our efforts at developing tools designed to monitor and redirect splicing helped assess the impact of misregulated splicing in cancer.
Research Interests:
Alternative splicing is the main source of proteome diversity. Here, we have investigated how alternative splicing affects the function of two human histone methyltransferases (HMTase): G9A and SUV39H2. We show that exon 10 in G9A and... more
Alternative splicing is the main source of proteome diversity. Here, we have investigated how alternative splicing affects the function of two human histone methyltransferases (HMTase): G9A and SUV39H2. We show that exon 10 in G9A and exon 3 in SUV39H2 are alternatively included in a variety of tissues and cell lines, as well as in a different species. The production of these variants is likely tightly regulated because both constitutive and alternative splicing factors control their splicing profiles. Based on this evidence, we have assessed the link between the inclusion of these exons and the activity of both enzymes. We document that these HMTase genes yield several protein isoforms, which are likely issued from alternative splicing regulation. We demonstrate that inclusion of SUV39H2 exon 3 is a determinant of the stability, the sub-nuclear localization, and the HMTase activity. Genome-wide expression analysis further revealed that alternative inclusion of SUV39H2 exon 3 differ...
Research Interests:
The mammalian proteins hnRNP A1 and hnRNP H control many splicing decisions in viral and cellular primary transcripts. To explain some of these activities, we have proposed that self-interactions between bound proteins create an RNA loop... more
The mammalian proteins hnRNP A1 and hnRNP H control many splicing decisions in viral and cellular primary transcripts. To explain some of these activities, we have proposed that self-interactions between bound proteins create an RNA loop that represses internal splice sites while simultaneously activating the external sites that are brought in closer proximity. Here we show that a variety of hnRNP H binding sites can affect 5' splice site selection. The addition of two sets of hnRNP H sites in a model pre-mRNA modulates 5' splice site selection cooperatively, consistent with the looping model. Notably, binding sites for hnRNP A1 and H on the same pre-mRNA can similarly collaborate to modulate 5' splice site selection. The C-terminal portion of hnRNP H that contains the glycine-rich domains (GRD) is essential for splicing activity, and it can be functionally replaced by the GRD of hnRNP A1. Finally, we used the bioluminescence resonance energy transfer (BRET) technology t...
Research Interests:
The control of alternative pre-mRNA splicing often requires the participation of factors displaying synergistic or antagonistic activities. In the hnRNP A1 pre-mRNA, three elements promote the exclusion of alternative exon 7B, while a... more
The control of alternative pre-mRNA splicing often requires the participation of factors displaying synergistic or antagonistic activities. In the hnRNP A1 pre-mRNA, three elements promote the exclusion of alternative exon 7B, while a fourth intron element (CE9) represses splicing of exon 7B to the downstream exon. We have shown previously that the 5' portion of the 38-nucleotide-long CE9 element is bound by SRp30c, and that this interaction is important for repression in vitro. To determine whether SRp30c alone can impose repression, we tested a high-affinity SRp30c binding site that we identified using the SELEX protocol. We find that multiple high-affinity SRp30c sites are required to replicate the level of repression obtained with CE9, and that both the 5' and the 3' portions of CE9 contribute to SRp30c binding. Performing RNA affinity chromatography with the complete CE9 element recovered hnRNP I/PTB. Surprisingly however, His-tagged PTB reduced the binding of SRp30...
Research Interests:
High-affinity binding sites for the hnRNP A1 protein stimulate the use of a distal 5' splice site in mammalian pre-mRNAs. Notably, strong A1-mediated shifts in splice site selection are not accompanied by equivalent changes in the... more
High-affinity binding sites for the hnRNP A1 protein stimulate the use of a distal 5' splice site in mammalian pre-mRNAs. Notably, strong A1-mediated shifts in splice site selection are not accompanied by equivalent changes in the assembly of U1 snRNP-containing complexes on competing 5' splice sites. To explain the above results, we have proposed that an interaction between hnRNP A1 molecules bound to high-affinity sites loops out the internal 5' splice site. Here, we present additional evidence in support of the looping out model. First, replacing A1 binding sites with sequences that can generate a loop through RNA duplex formation activates distal 5' splice site usage in an equivalent manner. Second, increasing the distance between the internal 5' splice site and flanking A1 binding sites does not compromise activation of the distal 5' splice site. Similar results were obtained with pre-mRNAs carrying inverted repeats. Using a pre-mRNA containing only one ...
Research Interests:
Several intron elements influence exon 7B skipping in the mammalian hnRNP A1 pre-mRNA. We have shown previously that the 38-nucleotide CE9 element located in the intron separating alternative exon 7B from exon 8 can repress the use of a... more
Several intron elements influence exon 7B skipping in the mammalian hnRNP A1 pre-mRNA. We have shown previously that the 38-nucleotide CE9 element located in the intron separating alternative exon 7B from exon 8 can repress the use of a downstream 3' splice site. The ability of CE9 to act on heterologous substrates, combined with the results of competition and gel shift assays, indicates that the activity of CE9 is mediated by a trans-acting factor. UV cross-linking analysis revealed the specific association of a 25-kDa nuclear protein with CE9. Using RNA affinity chromatography, we isolated a 25-kDa protein that binds to CE9 RNA. This protein corresponds to SRp30c. Consistent with a role for SRp30c in the activity of CE9, recombinant SRp30c interacts specifically with CE9 and can promote splicing repression in vitro in a CE9-dependent manner. The closest homologue of SRp30c, ASF/SF2, does not bind to CE9 and does not repress splicing even when the intronic SRp30c binding sites ...
Research Interests:
The hnRNP A1 pre-mRNA is alternatively spliced to yield the A1 and A1b mRNAs, which encode proteins differing in their ability to modulate 5' splice site selection. Sequencing a genomic portion of the murine A1 gene revealed that the... more
The hnRNP A1 pre-mRNA is alternatively spliced to yield the A1 and A1b mRNAs, which encode proteins differing in their ability to modulate 5' splice site selection. Sequencing a genomic portion of the murine A1 gene revealed that the intron separating exon 7 and the alternative exon 7B is highly conserved between mouse and human. In vitro splicing assays indicate that a conserved element (CE1) from the central portion of the intron shifts selection toward the distal donor site when positioned in between the 5' splice sites of exon 7 and 7B. In vivo, the CE1 element promotes exon 7B skipping. A 17-nucleotide sequence within CE1 (CE1a) is sufficient to activate the distal 5' splice site. RNase T1 protection/immunoprecipitation assays indicate that hnRNP A1 binds to CE1a, which contains the sequence UAGAGU, a close match to the reported optimal A1 binding site, UAGGGU. Replacing CE1a by different oligonucleotides carrying the sequence UAGAGU or UAGGGU maintains the preferen...
Research Interests:
Exon 7B in the hnRNP A1 pre-mRNA is alternatively spliced to yield A1 and A1(B), two proteins that differ in their ability to modulate 5' splice site selection. Sequencing the murine intron downstream of exon 7B revealed the existence... more
Exon 7B in the hnRNP A1 pre-mRNA is alternatively spliced to yield A1 and A1(B), two proteins that differ in their ability to modulate 5' splice site selection. Sequencing the murine intron downstream of exon 7B revealed the existence of several regions of similarity to the corresponding human intron. In vitro splicing assays indicate that an 84-nt region (CE6IO) decreases splicing to the proximal 5' splice site in a pre-mRNA carrying the 5' splice sites of exon 7 and 7B. In vivo, the CE6IO element promotes exon 7B skipping in pre-mRNAs expressed from a mini-gene containing the hnRNP A1 alternative splicing unit. Using oligonucleotide-targeted RNase H cleavage assays, we provide support for the existence of highly stable base pairing interactions between CE6IO and the 5' splice site region of exon 7B. Duplex formation occurs in naked pre-mRNA, resists incubation in splicing extracts, and is associated with a reduction in the assembly of U1 snRNP-dependent complexes t...
Research Interests:
Protection experiments with antibodies against small nuclear ribonucleoproteins (snRNPs) have elucidated the location of and requirements for interactions between snRNPs and human beta-globin transcripts during splicing in vitro. U2 snRNP... more
Protection experiments with antibodies against small nuclear ribonucleoproteins (snRNPs) have elucidated the location of and requirements for interactions between snRNPs and human beta-globin transcripts during splicing in vitro. U2 snRNP association with the intron branch site continues after branch formation, requires intact U2 RNA, and is affected by some alterations of the 3' splice site sequence. U2 snRNP binding to the branched intermediate and U1 snRNP protection of an extended 5' splice region are detected exclusively in spliceosome fractions, indicating that both snRNPs are spliceosome components. While each snRNP associates specifically with the pre-mRNA, they also appear to interact with each other. The recovery of fragments mapping upstream of the 5' splice site suggests how the excised exon is held in the spliceosome.
Research Interests:
A component present in splicing extracts selectively binds the 3' splice site of a precursor messenger RNA (pre-mRNA) transcript of a human beta-globin gene. Since this component can be immunoprecipitated by either autoantibodies of... more
A component present in splicing extracts selectively binds the 3' splice site of a precursor messenger RNA (pre-mRNA) transcript of a human beta-globin gene. Since this component can be immunoprecipitated by either autoantibodies of the Sm class or antibodies specifically directed against trimethylguanosine, it is a small nuclear ribonucleoprotein (snRNP). Its interaction with the 3' splice site occurs rapidly even at 0 degrees C, does not require adenosine triphosphate, and is altered by certain mutations in the 3' splice site region. Binding is surprisingly insensitive to treatment of the extract with micrococcal nuclease. The U5 particle is the only abundant Sm snRNP with a capped 5' end that is equally resistant to micrococcal nuclease. This suggests that, in addition to the U1 and U2 snRNP's, U5 snRNP's participate in pre-mRNA splicing.
Research Interests:
Research Interests:
Research Interests:
Telomeric DNA of mammalian chromosomes consists of several kilobase-pairs of tandemly repeated sequences with a terminal 3' overhang in single-stranded form. Maintaining the integrity of these repeats is essential for cell survival;... more
Telomeric DNA of mammalian chromosomes consists of several kilobase-pairs of tandemly repeated sequences with a terminal 3' overhang in single-stranded form. Maintaining the integrity of these repeats is essential for cell survival; telomere attrition is associated with chromosome instability and cell senescence, whereas stabilization of telomere length correlates with the immortalization of somatic cells. Telomere elongation is carried out by telomerase, an RNA-dependent DNA polymerase which adds single-stranded TAGGGT repeats to the 3' ends of chromosomes. While proteins that associate with single-stranded telomeric repeats can influence tract lengths in yeast, equivalent factors have not yet been identified in vertebrates. Here, it is shown that the heterogeneous nuclear ribonucleoprotein A1 participates in telomere biogenesis. A mouse cell line deficient in A1 expression harbours telomeres that are shorter than those of a related cell line expressing normal levels of A1....
Research Interests:
We previously described the use of tailed oligonucleotides as a means of reprogramming alternative pre-mRNA splicing in vitro and in vivo. The tailed oligonucleotides that were used interfere with splicing because they contain a portion... more
We previously described the use of tailed oligonucleotides as a means of reprogramming alternative pre-mRNA splicing in vitro and in vivo. The tailed oligonucleotides that were used interfere with splicing because they contain a portion complementary to sequences immediately upstream of the target 5' splice site combined with a non-hybridizing 5' tail carrying binding sites for the hnRNP A1/A2 proteins. In the present study, we have tested the inhibitory activity of RNA oligonucleotides carrying different tail structures. We show that an oligonucleotide with a 5' tail containing the human beta-globin branch site sequence inhibits the use of the 5' splice site of Bcl-xL, albeit less efficiently than a tail containing binding sites for the hnRNP A1/A2 proteins. A branch site-containing tail positioned at the 3' end of the oligonucleotide also elicited splicing inhibition but not as efficiently as a 5' tail. The interfering activity of a 3' tail was improved...