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Global analysis of binding sites of U2AF1 and ZRSR2 reveals RNA elements required for mutually exclusive splicing by the U2- and U12-type spliceosome

ABSTRACT: Eukaryotic nuclear introns have been dichotomously classified into common U2-type introns and rare U12-type introns. Because the highly conserved consensus sequences for the 5’ splice site and the branch point are found within all U12-type introns, weighted matrices for these motifs are used for prediction of U12-type introns. However, the U12-type consensus sequences per se are also recognized by the U2-type spliceosome. To better understand how distinct splicing systems recognize their authentic splice sites, we determined the binding sites of splicing factors, U2AF1 and ZRSR2, and found that ZRSR2 binding is mostly limited to U12-type introns. Our results reveal RNA elements contributing to selection of U2-type and U12-type splice sites in a mutually exclusive manner.

ORGANISM(S): Homo sapiens

PROVIDER: GSE203531 | GEO | 2022/05/24

REPOSITORIES: GEO

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Project description:U12-type introns were originally recognized based on their highly conserved non-consensus AT-AC termini1,2, which are spliced by a separate minor spliceosome3,4. Padgett and Krainer groups later showed that terminal dinucleotides do not differentiate U12-type from U2-type introns, as there are U12-type introns with GT-AG termini and U2-type introns with AT-AC termini5,6. Rather, U12-type introns are recognized by their divergent and highly conserved 5’ splice site (5’ss) and branch point sequences, which both differ from the consensus sequences found in U2-type introns. To date, no functional differences have been ascribed to AT-AC or GT-AG subtypes of U12-type introns, nor have RNAseq analyses of minor spliceosome diseases reported any subtype specificity. Here, we describe a novel protein component of the minor spliceosome, encoded by the CENATAC locus, that is required for accurate splicing of AT-AC but not GT-AG type minor introns. CENATAC was initially identified in a subset of Mosaic Variegated Aneuploidy (MVA) patients with mutations in CENATAC, which lead to chromosome congression defects during mitosis. Earlier large-scale proteomic analyses tentatively classified CENATAC as a spliceosome component and phylogenetic analyses showed co-segregation of CENATAC with minor spliceosome components. Targeted depletion of CENATAC in HeLa cells, followed by RNAseq revealed global retention of AT-AC minor subtype introns with more than 60% showing statistically significant (up to 90%) intron retention (IR). Additionally, U12-type introns with 5’-AT, but divergent 3’-terminal dinucleotides also showed significant IR. We also detected cryptic U2-type splice site activation near affected AT-AC introns. In contrast, about 10% of GT-AG subtype introns responded to CENATAC depletion. Co-IP experiments revealed that CENATAC is not a U11/U12 di-snRNP component as expected for a specificity factor, but rather associates with the U4atac/U6atac.U5 tri-snRNP via interaction with PRPF3/4, suggesting a role for minor tri-snRNP in initial 5’ss recognition. CENATAC also interacts with TXNL4B, a paralog of TXNL4A in the major tri-snRNP. Finally, several genes encoding chromosome congression factors harbor U12 AT-AC-type introns that were highly retained in CENATAC depleted cells, potentially explaining the aneuploidy phenotype observed in MVA patients.

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Global analysis of binding sites of U2AF1 and ZRSR2 reveals RNA elements required for mutually exclusive splicing by the U2- and U12-type spliceosome

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