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PubMed1987

Splicing of SV40 early pre-mRNA to large T and small t mRNAs utilizes different patterns of lariat branch sites.

To explore the mechanism and control of alternative splicing, we have characterized the products formed by splicing of SV40 early pre-mRNA in vitro and in vivo. Large T and small t mRNAs are derived from this precursor by joining alternative 5' splice sites to a single shared 3' splice site. In contrast to pre-mRNAs studied previously, we have shown that splicing to large T RNA involves the utilization of multiple lariat branch sites, while small t splicing uses a single branch site. Interestingly, the predominant branch sites utilized in splicing of large T RNA in vitro were found to differ in nuclear extracts from HeLa and human 293 cells, correlated with previously observed differences in the ratio of large T to small t mRNAs produced in the two cell types. To test the significance of this correlation, we examined the products formed by splicing of an SV40 early precursor microinjected into X. laevis oocytes. Strikingly, both the pattern of branch sites used in large T splicing and the ratio of large T to small t mRNAs produced were found to be identical to those observed in 293 cells and extracts.

Animals↗
PubMed1994

Tissue-specific alternative splicing of neurofibromatosis 1 (NF1) mRNA.

The neurofibromatosis 1 gene NF1 appears to play a crucial role in regulating the proliferation of cells of neural crest origin. The NF1 gene is a 300 kbp gene, encoding a complex pattern of mRNA related to the presence or absence of two alternative splices. The first splice, in the centre of the coding region of the gene, results in the addition of 63 bp in the GAP-related domain. The second splice located 4203 bp downstream, near the 3' terminus of the coding region of the gene, consists of a 54 bp insert. RT-PCR analysis demonstrates that the most prevalent splice variant in human tissues is the one which contains the GAP-related splice and omits the 3' terminal splice. It is also the form expressed in the peripheral nerve, adrenal medulla, benign NF1 neurofibromas and NF1 neurosarcomas. Conversely, a few organs (brain, muscle) exhibit extensive alternative splicing leading to the co-expression of four distinct transcripts. The reproducibility of the relative levels of each of the splice types in the different organs indicates a tissue-specific splicing pattern of the NF1 gene.

Alternative Splicing↗
PubMed2005

Brain-specific change in alternative splicing of Tau exon 6 in myotonic dystrophy type 1.

Alternative splicing is altered in myotonic dystrophy of type 1 (DM1), a syndrome caused by an increase of CTG triplet repeats in the 3' untranslated region of the myotonic dystrophy protein kinase gene. Previously, we reported the preferential skipping of Tau exon 2 in DM1 brains. In this study, we analyze the alternative splicing of Tau exon 6 which can be inserted in three different forms (c, p and d) depending on the 3' splice site used. In fact, inclusion of exon 6c decreases in DM1 brains compared to control brains whereas inclusion of 6d increases. Alteration of exon 6 splicing was not observed in DM1 muscle although this exon was inserted in RNAs from normal muscle and DM1 splicing alterations were first described in this organ. In contrast, alteration of exon 2 of Tau mRNA was observed in both muscle and brain. However, co-transfections of a minigene containing exon 6 with CELF or MBNL1 cDNAs, two splicing factor families suspected to be involved in DM1, showed that they influence exon 6 splicing. Altogether, these results show the importance of determining all the exons and organs targeted by mis-splicing to determine the dysregulation mechanisms of mis-splicing in DM1.

Alternative Splicing↗
PubMed2004

Alternative splicing of fibronectin: a mouse model demonstrates the identity of in vitro and in vivo systems and the processing autonomy of regulated exons in adult mice.

We have designed a novel approach using genetically engineered mice to make a systematic study of the EDA exon regulation of the fibronectin gene during development and aging. The genome of the mice was modified either by optimization of the EDA natural splice sites or by deleting the EDA region. The previous in vitro observation that the optimization of the splicing sites leads to constitutive inclusion of the EDA exon was confirmed in our animal model. In fact, all the adult tissues of the genetically modified mice showed only EDA(+) FN mRNA, demonstrating the fidelity of in vitro models, despite of the development- and aging-regulated splicing regulation of the EDA exon, and regardless of the presence of exonic elements described within the exon. This result indicates that the splicing regulatory elements of the EDA exon are dispensable in the presence of consensus splicing sites. Moreover, we demonstrate the autonomy of both the EDB and the IIICS alternatively spliced regions in adult mice lacking regulation of the alternative splicing at the EDA exon. We also show here the tight splicing regulation of all three alternative spliced regions of the FN gene at different time-points during development and aging of mice.

Alternative Splicing↗
PubMed2006

Alternative splicing in human transcriptome: functional and structural influence on proteins.

Alternative splicing is a molecular mechanism that produces multiple proteins from a single gene, and is thought to produce variety in proteins translated from a limited number of genes. Here we analyzed how alternative splicing produced variety in protein structure and function, by using human full-length cDNAs on the assumption that all of the alternatively spliced mRNAs were translated to proteins. We found that the length of alternatively spliced amino acid sequences, in most cases, fell into a size shorter than that of average protein domain. We evaluated comprehensively the presumptive three-dimensional structures of the alternatively spliced products to assess the impact of alternative splicing on gene function. We found that more than half of the products encoded proteins which were involved in signal transduction, transcription and translation, and more than half of alternatively spliced regions comprised interaction sites between proteins and their binding partners, including substrates, DNA/RNA, and other proteins. Intriguingly, 67% of the alternatively spliced isoforms showed significant alterations to regions of the protein structural core, which likely resulted in large conformational change. Based on those findings, we speculate that there are a large number of cases that alternative splicing modulates protein networks through significant alteration in protein conformation.

Alternative Splicing↗
PubMed2005

SL trans-splicing: easy come or easy go?

Is spliced-leader (SL) trans-splicing an ancestral eukaryotic characteristic that has been lost in multiple lineages, or did it arise independently in the various phyla in which it occurs? Recent studies have discovered SL trans-splicing in new metazoan phyla, including the chordates. Its discovery in chordates identifies, for the first time, a phylum that clearly contains both trans-splicing and non-trans-splicing major groups, and defines a limited and well-understood field in which to study the evolutionary dynamics of SL trans-splicing. In this article, I summarize the evolutionarily relevant aspects of SL trans-splicing and consider the interplay among SL trans-splicing, pre-mRNA splice-signal syntax and evolutionary genomics.

Animals↗
PubMed2002

Two distinct functional spliced leader RNA gene arrays in Leishmania tarentolae are found in several lizard Leishmania species.

A second distinct array of spliced leader RNA genes has been found in several Leishmania species particular to lizards. This is the first report of two non-allelic arrays of spliced leader RNA genes within a species cell line. The arrays are identical to each other in their transcribed spliced leader RNA gene sequences, but variable in their non-transcribed spacer sequences. In the two arrays from Leishmania tarentolae UC strain the promoter regions are similar, but not identical, at positions shown previously to be critical for spliced leader RNA transcription. These arrays contain similar numbers of genes and are both transcribed in L. tarentolae in vitro transcription extract as well as in vivo. The -66/-58 regions of both genes, which contain an element of the spliced leader RNA gene promoter, bind proteins likely to be transcription factors in a specific manner. A survey of lizard Leishmania spp. revealed a second spliced leader RNA gene array in three of four species. Phylogenetic analyses of these sequences with each other and with the spliced leader RNA gene sequences of non-lizard Leishmania spp. and their near-relatives showed that the lizard groups are more closely related to each other than to arrays from other Leishmania spp. As the transcripts of the two arrays are identical, they may co-exist to fulfil the substantial requirement for spliced leader RNA production; however, they have the potential for differential usage modulated by their distinct promoter elements. The presence of two distinct spliced leader RNA gene arrays within a single cell type may represent dissociated evolution of two redundant loci, or a previously unsuspected level of control in the post-transcriptional gene expression within some kinetoplastids.

Alleles↗
PubMed1985

Trans splicing of mRNA precursors in vitro.

Two exon segments from two separate RNA molecules can be joined in a trans splicing process. In trans splicing reactions, an RNA molecule containing an exon, a 5' splice site, and adjacent intron sequences was mixed with an RNA molecule containing an exon, a 3' splice site, and adjacent intron sequences. The efficiency of trans splicing of these two RNAs increased if the two termini of the intervening sequences were paired in a short RNA duplex. However, trans splicing of two RNA molecules with no significant complementarity was also observed. These results strongly suggest that significant secondary structures within intervening sequences could affect the splicing of flanking exons. Similarly, RNAs that are complementary to segments within the intervening sequences could potentially regulate the selection of splice sites. Finally, some organisms might use trans splicing to distribute a single exon to many different mRNAs.

Adenosine Triphosphate↗
PubMed1999

TRAF-3 mRNA splice-deletion variants encode isoforms that induce NF-kappaB activation.

Although TRAF-3 gene products are required for signaling in T-B cell collaboration, full-length TRAF-3 appears to lack signaling function in transient transfection assays that measure NF-kappaB activation. However, the TRAF-3 gene also encodes at least three mRNA splice-deletion variants that predict protein isoforms (delta25aa, delta52aa and delta56aa) with altered zinc (Zn) finger domains and unknown functional capacities. To determine whether TRAF-3 splice-deletion variants may transmit activating receptor signals to the nucleus, cDNAs for five additional splice-variant isoforms (delta27aa, delta83aa, delta103aa, delta130aa and delta221aa) were cloned from a TRAF-3+ lymphoma and the expression and function of each of the eight TRAF-3 splice-deletion variants was analyzed. Among the splice-deletion variants, TRAF-3 delta130 mRNA is expressed by tonsillar B cells and by each of a panel of B and T cell lines. TRAF-3 delta221 protein is expressed by tonsillar B cells and by each of the lymphocytic lines. The functional effect of over-expressing each TRAF-3 splice-deletion variant on NF-kappaB activation was studied in 293 T cells. Seven of the TRAF-3 splice-deletion variants, such as TRAF-3 delta130, induce substantial NF-kappaB-driven luciferase activity (80-500 fold). In contrast, TRAF-3 delta221 (in which the complete Zn finger domain is absent) fails to induce NF-kappaB activation. Although full-length TRAF-3 alone is inactive, it augments the functional effects of the seven activating TRAF-3 splice-deletion variants (1.4-5 fold). These data indicate that alterations of the Zn finger domains render the TRAF-3 splice-deletion variants capable of inducing NF-kappaB activation and that full-length TRAF-3 augments their signaling.

Alternative Splicing↗
PubMed1997

Gene linkage and steady state RNAs suggest trans-splicing may be associated with a polycistronic transcript in Schistosoma mansoni.

Spliced leader (SL) trans-splicing generates the 5' end of mature mRNAs through the addition of a small exon to pre-mRNAs in some flagellates (kinetoplastida and euglenoids) and metazoans (nematodes and flatworms). Although SL addition in the kinetoplastida and a subset of nematode genes serves to resolve multicistronic mRNAs into monocistronic, capped mRNAs, information regarding the functional significance of trans-splicing in flatworms is limited. We describe here the identification and characterization of a closely linked gene upstream from the trans-spliced enolase gene in the flatworm Schistosoma mansoni. This gene produces a non-trans-spliced mRNA encoding a ubiquinol binding protein, UbCRBP, that is a component of the ubiquinol-cytochrome C reductase complex. The distance between the UbCRBP polyadenylation site and the enolase trans-splice acceptor site is exceptionally short, only 54 nucleotides. Primer extension (5' RACE), RT-PCR, and RNase mapping have identified steady state, cis-spliced RNAs which significantly overlap both the UbCRBP and enolase genes. These transcripts contain the 5' ends of mature UbCRBP mRNAs; extend through UbCRBP, across the intergenic region, and a significant distance 3' into the enolase gene. Interestingly, the close linkage between the UbCRBP and enolase genes is conserved in a second flatworm, Fasciola hepatica, which also trans-splices the downstream enolase gene. Taken together, the role of SL addition in resolving multicistronic transcripts in both C. elegans and the kinetoplastida, the conservation of UbCRBP/enolase gene linkage in two divergent trematodes, and the multicistronic organization of schistosome UbCRBP/enolase RNAs are consistent with the suggestion that these two genes are likely to be cotranscribed and that trans-splicing in flatworms may be associated with polycistronic transcripts.

Amino Acid Sequence↗
PubMed2001

Quantitative mRNA analysis of five C-terminal splice variants of the human 5-HT4 receptor in the central nervous system by TaqMan real time RT-PCR.

5-HT4 receptors mediate several physiological effects of 5-HT, particularly in the central nervous system (CNS), heart and gut. Recently, several C-terminal splice variants of the human 5-HT4 (h5-HT4) receptor have been described, namely h5-HT4(a), h5-HT4(b), h5-HT4(c), h5-HT4(d) and h5-HT4(g). Previous tissue distribution data suggest some degree of specificity in the mRNA expression patterns of the different h5-HT4 receptor splice variants. However, comparison of the mRNA expression profiles of these splice variants is difficult due to the non-quantitative methods used, and in addition, there is very limited data on the expression of each splice variant in human CNS subregions. In the present study we used a single technique, TaqMan real time quantitative RT-PCR, to investigate the mRNA distribution of 5-HT4 receptor C-terminal splice variants in multiple human CNS and peripheral tissues. Using a primer/probe set that amplified all 5-HT4 splice variants (5-HT4pan), the highest CNS expression of 5-HT4 receptor mRNA was observed in basal ganglia, amygdala and hippocampus, consistent with previous studies. h5-HT4(a), h5-HT4(b), h5-HT4(c) and h5-HT4(g) were predominantly expressed in various CNS tissues, compared to most peripheral tissues, but there were differences in expression levels and distribution patterns of each variant. The distribution profile and expression levels observed for the 5-HT4(b) splice variant were virtually identical to that obtained with the 5-HT4pan primer/probe set, whilst the other splice variants were expressed at much lower levels and with different expression patterns obtained with both 5-HT4(b) and 5-HT4pan primer/probe sets. Highest levels of 5-HT4(g) were observed in the hypothalamus and cortex, whilst the 5-HT4(a) variant was highest in the amygdala. 5-HT4(c) expression was highest in the pituitary gland whilst 5-HT4(d) mRNA was only detected in the small intestine at very low levels and not in the CNS. In conclusion, we have shown quantitative differences in the mRNA distribution profiles of the 5-HT4 receptor C-terminal splice variants in human CNS subregions as well as peripheral tissues. In addition, our data suggests that the h5-HT4(b) variant is the most predominant form of the 5-HT4 receptor in humans.

Alternative Splicing↗
PubMed1997

Developmental regulation and cell-specific expression of N-methyl-D-aspartate receptor splice variants in rat hippocampus.

The present study demonstrates cell-specific and developmental regulation of 5' and 3' splicing of the N-methyl-D-aspartate receptor NR1 subunit within specific neuronal populations of the hippocampus. At birth, NR1 transcripts lacking exon 5 (encoding the amino-terminal splice cassette N1) exhibit mature patterns of labelling within the hippocampus, with high levels of expression in the CA1, CA3, and dentate gyrus. In contrast, exon 5-containing (NR1(1XX)) transcripts are expressed at low levels until P8, at which time expression is prominent and essentially uniform in the CA1, CA3, and dentate gyrus. Exon 5 expression increases at a faster rate in CA3 than in CA1 or dentate gyrus. By the third week postnatal (postnatal day P21), exon 5-containing transcripts exhibit a distinct gradient of labelling, with more intense expression in CA3, than in CA1 or dentate gyrus. By P21 pyramidal neurons of the CA1 and granule cells of the dentate gyrus express mainly NR1(0XX) receptor messenger RNAs (lacking exon 5). Because splicing in of the N1 splice cassette confers greater current amplitude and enhanced potentiation by protein kinase C, these observations predict elevated levels of synaptic activity in the CA1 early in postnatal life, a time at which synaptic plasticity is enhanced. The carboxy-terminal splice cassettes C1 and C2 are regulated independently within the hippocampus. Whereas NR1(X11) (C1-, C2-containing) and NR1(X01) (C2 only) receptors exhibit high levels of expression in CA1, CA3, and dentate gyrus, NR1(X00) receptors are expressed more intensely in pyramidal neurons of CA3. NR1(X10) receptor expression is very low in all cells and at all times examined, even in adults. Because splicing in of the C1 cassette is thought to regulate receptor targeting, clustering, and cytoskeletal interactions, N-methyl-D-aspartate receptors in the two hippocampal subfields may play differing roles in synaptogenesis and the formation of new neuronal contacts. Moreover, cell-specific patterns of NR1(X11) receptor messenger RNAs parallel those of NR1(0XX) receptor messenger RNAs; and cell-specific patterns of NR1(1XX) (N1-containing) receptor messenger RNAs parallels those of NR1(X00) (C1-, C2-lacking) receptor messenger RNAs throughout development. These observations suggest that NR1(100) receptors, which exhibits the greatest potentiation by protein kinase C, are likely to be important in CA1 during the second and third weeks postnatal. Cell-specific expression of NR1 splice variants undoubtedly contributes to functional diversity of N-methyl-D-aspartate receptor properties in neuronal populations within the hippocampus. Developmental regulation of NR1 splicing is likely to influence synaptic plasticity and the formation of new synaptic contacts. Moreover, findings from this study suggest that a change in NR1 splicing following a neurological injury could significantly alter glutamate pathogenicity in a particular population of cells.

Animals↗
PubMed1997

Stage-independent splicing of transcripts two heterogeneous neighboring genes in Leishmania amazonensis.

Gene expression in trypanosomatid protozoa is largely regulated posttranscriptionally, e.g., 5' splice leader addition and 3' polyadenylation of mRNAs. We examined these events in Leishmania by mapping the splice sites of the transcripts from two different, but closely linked single-copy genes 2.3 kb apart. The coding regions of the approx. 1 kb upstream gene (P36) and the approx. 1.4 kb downstream gene (NAGT) produce approx. 2 and 3 kb mRNAs, respectively. Both genes were overexpressed in cells that were transfected with this bicistronic unit (> or = 7.5 kb), taking advantage of the NAGT as a selectable marker for tunicamycin-resistance. The transcripts from both genes were spliced constitutively at both ends, irrespective of their episomal or chromosomal expression in both leishmanial stages. Primer extension of the 5' UTRs and S1 nuclease protection of the 3' UTRs initially identified the major splice sites, corresponding to the genomic sequence at -205 bp and + approx. 900 bp of P36, and -1012 bp and + approx. 600 bp of NAGT. These splice sites, consistent with the size of the major transcripts, are among those mapped precisely by sequencing RT-PCR amplified 5' and 3' UTRs. The additional sites mapped by the latter are minor alternatives, especially abundant for transcripts of the downstream NAGT. All these minor splice sites are closer than the major splice sites to the coding region, indicating that the most distant splice sites are preferentially used. This preference creates a 387 bp 'gap' with polypyrimidine tracts in the intergenic region consistent with the model coupling splice leader addition with polyadenylation in pre-mRNA processing. The stage-independence of these events suggests that the 7.5 kb dicistronic unit is suitable for constructing Leishmania-specific constitutive expression vectors.

Animals↗
PubMed2001

A purine-rich intronic element enhances alternative splicing of thyroid hormone receptor mRNA.

The mammalian thyroid hormone receptor gene c-erbAalpha gives rise to two mRNAs that code for distinct isoforms, TRalpha1 and TRalpha2, with antagonistic functions. Alternative processing of these mRNAs involves the mutually exclusive use of a TRalpha1-specific polyadenylation site or TRalpha2-specific 5' splice site. A previous investigation of TRalpha minigene expression defined a critical role for the TRalpha2 5' splice site in directing alternative processing. Mutational analysis reported here shows that purine residues within a highly conserved intronic element, SEa2, enhance splicing of TRalpha2 in vitro as well as in vivo. Although SEalpha2 is located within the intron of TRalpha2 mRNA, it activates splicing of a heterologous dsx pre-mRNA when located in the downstream exon. Competition with wild-type and mutant RNAs indicates that SEalpha2 functions by binding trans-acting factors in HeLa nuclear extract. Protein-RNA crosslinking identifies several proteins, including SF2/ASF and hnRNP H, that bind specifically to SEalpha2. SEalpha2 also includes an element resembling a 5' splice site consensus sequence that is critical for splicing enhancer activity. Mutations within this pseudo-5' splice site sequence have a dramatic effect on splicing and protein binding. Thus SEa2 and its associated factors are required for splicing of TRalpha2 pre-mRNA.

Alternative Splicing↗
PubMed2001

Interplay between AAUAAA and the trans-splice site in processing of a Caenorhabditis elegans operon pre-mRNA.

About half of Caenorhabditis elegans genes have a 1-2 bp mismatch to the canonical AAUAAA hexamer that signals 3' end formation. One rare variant, AGUAAA, is found at the 3' end of the mai-1 gene, the first gene in an operon also containing gpd-2 and gpd-3. When we expressed this operon under heat shock control, 3' end formation dependent on the AGUAAA was very inefficient, but could be rescued by a single bp change to create a perfect AAUAAA. When AGUAAA was present, most 3' ends formed at a different site, 100 bp farther downstream, right at the gpd-2 trans-splice site. Surprisingly, 3' end formation at this site did not require any observable match to the AAUAAA consensus. It is possible that 3' end formation at this site occurs by a novel mechanism--trans-splicing-dependent cleavage--as deletion of the trans-splice site prevented 3' end formation here. Changing the AGUAAA to AAUAAA also influenced the trans-splicing process: with AGUAAA, most of the gpd-2 product was trans-spliced to SL1, rather than SL2, which is normally used at downstream operon trans-splice sites. However, with AAUAAA, SL2 trans-splicing of gpd-2 was increased. Our results imply that (1) the AAUAAA consensus controls 3' end formation frequency in C. elegans; (2) the AAUAAA is important in determining SL2 trans-splicing events more than 100 bp downstream; and (3) in some circumstances, 3' end formation may occur by a trans-splicing-dependent mechanism.

Animals↗
PubMed1993

Minimum intron requirements for tRNA splicing and nuclear transport in Xenopus oocytes.

The presence or absence of an intron defines two classes of eukaryotic nuclear tRNA genes whose transcripts differ in a requirement for splicing. Using quantitative nuclear microinjection, we have previously found that nucleocytoplasmic transport of these two classes of tRNAs involves pathways which differ in one or more limiting components. To examine substrate features which distinguish these two pathways, a series of variants of a Xenopus tRNA(Tyr) gene were constructed in which the intron size was altered. The splicing and transport properties of the resulting transcripts were examined in oocyte microinjection and in vitro processing assays. The addition of one or two nucleotides at the splice site equivalent in an intronless gene produced transcripts which could be transported without splicing. However, transport was reduced relative to the mature-sequence tRNA, suggesting the anticodon loop (interrupted in pre-tRNAs) may be recognized by the intronless tRNA transport apparatus. Transcripts with four- or six-nucleotide intervening sequences were incompletely spliced with cleavage at only the 3' splice site. Neither unspliced precursor nor partially processed intermediates were efficiently transported. The results of coinjection experiments using tRNA and pre-tRNA competitors suggest that simple retention by the splicing apparatus may not account for failure to export these RNAs. Finally, a requirement for splicing is not unique to transport of pre-tRNA(Tyr) since a pre-tRNA(3Leu) variant which was not spliced was also not exported.

Animals↗
PubMed1998

Regulation of adenovirus alternative RNA splicing by dephosphorylation of SR proteins.

SR proteins are a family of essential splicing factors required for early recognition of splice sites during spliceosome assembly. They also function as alternative RNA splicing factors when overexpressed in vivo or added in excess to extracts in vitro. SR proteins are highly phosphorylated in vivo, a modification that is required for their function in spliceosome assembly and splicing catalysis. Here we show that SR proteins purified from late adenovirus-infected cells are inactivated as splicing enhancer or splicing repressor proteins by virus-induced dephosphorylation. We further show that the virus-encoded protein E4-ORF4 activates dephosphorylation by protein phosphatase 2A of HeLa SR proteins and converts their splicing properties into that of SR proteins purified from late adenovirus-infected cells. Taken together, our results suggest that E4-ORF4 is an important factor controlling the temporal shift in adenovirus alternative RNA splicing. We conclude that alternative pre-mRNA splicing, like many other biological processes, is regulated by reversible protein phosphorylation.

Adenoviridae↗
PubMed1990

A 3' splice site-binding sequence in the catalytic core of a group I intron.

Ribozymes use specific RNA-RNA interactions for substrate binding and active-site formation. Self-splicing group I introns have approximately 70 nucleotides constituting the core, a region containing sequences and structures indispensable for catalytic function. The catalytic core must interact with the substrates used for the two steps of the self-splicing reaction, that is, guanosine, the 5'-splice-site helix (P1) and the 3' splice site. Mutational evidence suggests that core sequences near segment J6/7 that joins the base-paired stems P6 and P7, and the bulged base of P7(5'), participate in binding guanosine substrate, but nothing is known about the interactions between the core, the 5'-splice-site helix and the 3' splice site. On the basis of comparative sequence data, it has been suggested that two specific bases in the catalytic core of group I introns might form a binding sequence for the 3' splice site. Here we present genetic evidence that such a binding site exists in the core of the Tetrahymena large subunit ribosomal RNA intron. We demonstrate that this pairing, termed P9.0, is functionally important in the exon ligation step of self-splicing, but is not itself responsible for 3'-splice-site selection.

Animals↗