![]() ![]() Taking ALYREF as an example, it is unclear whether CBCA or the RNA splicing process serve to anchor ALYREF to the first exons of transcripts 13, 20, 21. ![]() While it is clear that the CBCA complex provides a basic platform for early factor recruitment, it remains elusive when and how these factors settle within their respective RNPs. Source data are provided as a Source Data file. In order to capture the spatial variance, whole TUs were segmented into 10 kb bins and treated as individual data points. e Principal component analysis (PCA) plot of tiCLIP data from mono (left)- and multi (right)-exonic TUs showing the variation across libraries. d Histograms showing average RBP binding densities (reads/kb) calculated from all exonic and intronic regions of mono- and multi-exonic transcription units (TUs) as indicated. ‘Negative’ timepoints represent controls in which blank magnetic beads were used (negative anti-GFP lanes) on unsynchronised samples. Numbers from individual biological replicates are shown as circles, squares and triangles. c Histograms showing the average number of normalised mapped tiCLIP reads. b Schematic outline of the tiCLIP approach (lower panel) as compared to regular steady state iCLIP (upper panel). Comprised of the MTR4, ZCCHC8 and RBM7 proteins, NEXT then recruits the ribonucleolytic RNA exosome to degrade a wide range of short non-adenylated transcripts and to process precursor forms of small RNAs, like snoRNAs, residing inside pre-mRNA introns 7, 15, 16, 17, 18, 19.Ī Simplified overview of the CBC and its two cofactors, ALYREF and RBM7, with relevance for the present study. One such adaptor is the trimeric Nuclear Exosome Targeting (NEXT) complex, which together with the ZC3H18 protein joins CBCA to form the CBC-NEXT (CBCN) complex 7. Adaptors of RNA decay factors are also loaded onto nascent transcripts to achieve RNA processing or complete degradation. the splicing process contributes to attract the human Transcription and Export complex (hTREX) component ALYREF is being debated 13, 14. For multi-exonic transcripts, their splicing was suggested to prepare the RNA for nuclear export 12 and the extent to which the CBCA complex vs. After productive transcription is initiated, the CBC is joined by the Arsenite resistance protein 2 (ARS2) to form the CBC-ARS2 (CBCA) complex 7, 10, 11, which then aids the recruitment of additional factors onto the nascent RNA (Fig. CBP80 in turn initiates the binding of proteins capable of directing the fate of the elongating RNA 2, 7, 8, 9. CBP20 binds nascent RNA after the transcript 5′end has received its hallmark 7-methylguanylate (m 7G) cap 6. This process initiates during transcription where early remodelling steps impact RNP formation 3, 4, 5.Īn early and omnipresent member of RNAPII-derived RNPs is the Cap Binding Complex (CBC) composed of CBP20 and CBP80. The early ribonucleoprotein (RNP) complex is acted upon by RNA processing-, transport- and decay-factors, which, dictated by transcript features, compete to shape RNP identity, while at the same time eliminate RNA processing by-products and mis- or excessively-produced material 1, 2. The fate of an RNA polymerase II (RNAPII)-transcribed RNA is impacted by its dynamic association with RNA-binding proteins (RBPs). Altogether, our data provide a temporal view of RNA-protein interactions during the early phases of transcription. Finally, we identify underappreciated steps in snoRNA 3′end processing performed by RBM7. Moreover, we demonstrate that the two transesterification steps of pre-mRNA splicing temporally separate ALYREF and RBM7 binding to splicing intermediates, and that exon-exon junction density drives RNA 5′end binding of ALYREF. Regardless of function, all tested factors interact with nascent RNA as it exits RNAPII. We apply tiCLIP to the RNA export adaptor, ALYREF a component of the Nuclear Exosome Targeting (NEXT) complex, RBM7 and the nuclear cap binding complex (CBC). To remedy this, we here conduct temporal-iCLIP (tiCLIP), combining RNAPII transcriptional synchronisation with UV cross-linking of RNA-protein complexes at serial timepoints. Yet, our current understanding of this process in vivo primarily stems from steady state analysis. Dynamic RNA-protein interactions govern the co-transcriptional packaging of RNA polymerase II (RNAPII)-derived transcripts. ![]()
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