Project description:UV cross-linking and immunoprecipitation (CLIP) and individual-nucleotide resolution CLIP (iCLIP) are the most frequently used methods to study protein-RNA interactions in the intact cells and tissues, but their relative advantages or inherent biases have not been evaluated. To benchmark CLIP and iCLIP method, we performed iCLIP with Nova protein, which is the most extensively studied protein by CLIP. Further, we assessed UV-C-induced cross-linking preferences, by exploiting the UV-independent formation of covalent RNA cross-links of the mutant RNA methylase NSUN2.
Project description:UV cross-linking and immunoprecipitation (CLIP) and individual-nucleotide resolution CLIP (iCLIP) are methods to study protein-RNA interactions in untreated cells and tissues. Here, we analyzed six published and two novel data sets to confirm that both methods identify protein-RNA cross-link sites, and to identify a slight uridine preference of UV-C-induced cross-linking. Comparing Nova CLIP and iCLIP data revealed that cDNA deletions have a preference for TTT motifs, whereas iCLIP cDNA truncations are more likely to identify clusters of YCAY motifs as the primary Nova binding sites. In conclusion, we demonstrate how each method impacts the analysis of protein-RNA binding specificity.
Project description:The identification of RNAs that are recognized by RNA-binding proteins (RNA-BPs) using techniques such as Crosslinking and Immunoprecipitation (CLIP) has revolutionized the genome-wide discovery of RNA-BP RNA targets. Among the different versions of CLIP that have been developed, the use of photoactivable nucleoside analogs has resulted in high efficiency photoactivable ribonucleoside-enhanced CLIP (PAR-CLIP) in vivo. Nonetheless, PAR-CLIP has not yet been applied in prokaryotes. To determine if PAR-CLIP can be used in prokaryotes, we determined suitable conditions for the incorporation of 4-thiouridine (4SU), a photoactivable nucleoside, into E. coli RNA and for the isolation of RNA crosslinked to RNA-BPs of interest. Applying this technique to Hfq, a well-characterized regulator of small RNA (sRNA)-messenger RNA (mRNA) interactions, we showed that PAR-CLIP identified most of the known sRNA targets of Hfq, as well as functionally relevant sites of Hfq-mRNA interactions at nucleotide resolution. Based on our findings, PAR-CLIP represents an improved method to identify both the RNAs and the specific regulatory sites that are recognized by RNA-BPs in prokaryotes.
Project description:UV-crosslinking and immunoprecipitation (CLIP) combined with high-throughput sequencing was previously used to generate transcriptome-wide binding maps of several RNA-binding proteins. However, since identification of binding sites relied on the analysis of overlapping sequence clusters, distances of less than 30 nucleotides were not resolved. An additional disadvantage of CLIP is the requirement of reverse transcription to pass over residual amino acids that remain covalently attached to the RNA at the crosslink site. Primer extension assays have shown that the vast majority of cDNAs prematurely truncate immediately before the 'crosslink nucleotide'. Here, we exploited this apparent limitation to achieve single nucleotide resolution by capturing these truncated cDNAs through the introduction of a second adapter after reverse transcription via self-circularization. In order to quantify cDNA molecules that truncate at the same nucleotide, we added a random barcode to the DNA adapter. This allowed us to discriminate between unique cDNA products and PCR duplicates . Taken together, individual-nucleotide resolution CLIP (iCLIP) enables precise mapping of protein-RNA interactions in intact cells. ArrayExpress Release Date: 2010-09-03 Publication Title: iCLIP reveals the function of hnRNP particles in splicing at individual nucleotide resolution Publication Author List: Konig J, Zarnack K, Rot G, Curk T, Kayikci M, Zupan B, Turner DJ, Luscombe NM, Ule J. Person Roles: submitter Person Last Name: Konig Person First Name: Julian Person Email: jkonig@mrc-lmb.cam.ac.uk Person Phone: 0044 7531 502686 Person Address: Hills Road, CB2 0QH Cambridge, UK Person Affiliation: MRC LMB
Project description:To better understand the mechanism of U1A functions in human cells, we performed U1A iCLIP-seq analysis in HeLa cells. iCLIP-seq is a previously well-established protocol that is believed to detect protein-RNA interaction at individual-nucleotide resolution. Indeed, successful completion of U1A iCLIP-seq has helped us to illuminate more detailed mechanism through which U1 snRNP prevents mRNA PCPA (premature cleavage and polyadenylation)
Project description:Purpose: to identify the AGO1-bound miRNAs and mRNAs in human endothelial cells subject to hypoxic condition (2% oxygen) Methods: human microvascular endothelial cells was cultured under normoxia (20% oxygen) or hypoxia (2%) oxygen for 24 hours. Total RNA was extracted and RNA and small RNA libraries were prepared for Seq. Results: We found substantial changes in AGO1-bound mRNAs due to hypoxia. A portion of CLIP-seq reads also reveal direct binding to miRNA to mRNA. Conclusions: hypoxia induces profound changes in mRNAs associated with AGO1.
Project description:Crosslinking and immunoprecipitation (CLIP) is increasingly used to map transcriptome-wide binding sites of RNA-binding proteins (RBPs). We developed a method for CLIP data analysis and applied it to compare 254 nm CLIP with PAR-CLIP, which involves crosslinking of photoreactive nucleotides with 365 nm UV light. We found small differences in the accuracy of these methods in identifying binding sites of HuR, a protein that binds low-complexity sequences and Argonaute 2, which has a complex binding specificity. We show that crosslink-induced mutations lead to single-nucleotide resolution for both PAR-CLIP and CLIP. Our results confirm the expectation from original CLIP publications that RNA-binding proteins do not protect sufficiently their sites under the denaturing conditions used during the CLIP procedure, and we show that extensive digestion with sequence-specific ribonucleases strongly biases the set of recovered binding sites. We finally show that this bias can be substantially reduced by milder nuclease digestion conditions. We performed duplicate experiments for each variant of the CLIP protocol (CLIP, PAR-CLIP), each protein (HuR, Ago2), and enzymatic digestion (complete T1 digestion, mild MNase digestion). In addition, we performed a single PAR-CLIP experiment with mild T1 digestion.
Project description:Crosslinking and immunoprecipitation (CLIP) is increasingly used to map transcriptome-wide binding sites of RNA-binding proteins (RBPs). We developed a method for CLIP data analysis and applied it to compare 254 nm CLIP with PAR-CLIP, which involves crosslinking of photoreactive nucleotides with 365 nm UV light. We found small differences in the accuracy of these methods in identifying binding sites of HuR, a protein that binds low-complexity sequences and Argonaute 2, which has a complex binding specificity. We show that crosslink-induced mutations lead to single-nucleotide resolution for both PAR-CLIP and CLIP. Our results confirm the expectation from original CLIP publications that RNA-binding proteins do not protect sufficiently their sites under the denaturing conditions used during the CLIP procedure, and we show that extensive digestion with sequence-specific ribonucleases strongly biases the set of recovered binding sites. We finally show that this bias can be substantially reduced by milder nuclease digestion conditions.
Project description:Individual-nucleotide resolution UV-crosslinking and immunoprecipitation (iCLIP) combined with high-throughput sequencing was used to generate a transcriptome-wide binding map of hnRNP L. Supplementary file GSE37560_hnRNPL_crosslink_site.bed includes filtered crosslink sites of hnRNPL: combining data from all 3 experiments.