Project description:Proteomic methods for RNA interactome capture (RIC) rely principally on crosslinking native or labeled cellular RNA to enrich and investigate RNA-binding protein (RBP) composition and function in cells. The ability to measure RBP activity at individual binding sites by RIC, however, has been more challenging due to the heterogenous nature of peptide adducts derived from the RNA-protein crosslinked site. Here, we present an orthogonal strategy that utilizes clickable electrophilic purines to directly quantify protein-RNA interactions on proteins through photoaffinity competition with 4-thiouridine (4SU)-labeled RNA in cells. Our photo-activatable-competition and chemoproteomic enrichment (PACCE) method facilitated detection of >5,500 cysteine sites across ~3,000 proteins displaying RNA-sensitive alterations in probe binding. Importantly, PACCE enabled functional profiling of canonical RNA-binding domains as well as discovery of moonlighting RNA binding activity in the human proteome. Collectively, we present a chemoproteomic platform for global quantification of protein-RNA binding activity in living cells.
Project description:Proteomic methods for RNA interactome capture (RIC) rely principally on crosslinking native or labeled cellular RNA to enrich and investigate RNA-binding protein (RBP) composition and function in cells. The ability to measure RBP activity at individual binding sites by RIC, however, has been more challenging due to the heterogenous nature of peptide adducts derived from the RNA-protein crosslinked site. Here, we present an orthogonal strategy that utilizes clickable electrophilic purines to directly quantify protein-RNA interactions on proteins through photoaffinity competition with 4-thiouridine (4SU)-labeled RNA in cells. Our photo-activatable-competition and chemoproteomic enrichment (PACCE) method facilitated detection of >5,500 cysteine sites across ~3,000 proteins displaying RNA-sensitive alterations in probe binding. Importantly, PACCE enabled functional profiling of canonical RNA-binding domains as well as discovery of moonlighting RNA binding activity in the human proteome. Collectively, we present a chemoproteomic platform for global quantification of protein-RNA binding activity in living cells.
Project description:RNA-binding proteins (RBPs) have essential roles in RNA-mediated gene regulation, and yet annotation of RBPs is limited mainly to those with known RNA-binding domains. To systematically identify the RBPs of embryonic stem cells (ESCs), we here employ interactome capture, which combines UV cross-linking of RBP to RNA in living cells, oligo(dT) capture and MS. From mouse ESCs (mESCs), we have defined 555 proteins constituting the mESC mRNA interactome, including 283 proteins not previously annotated as RBPs. Of these, 68 new RBP candidates are highly expressed in ESCs compared to differentiated cells, implicating a role in stem-cell physiology. Two well-known E3 ubiquitin ligases, Trim25 (also called Efp) and Trim71 (also called Lin41), are validated as RBPs, revealing a potential link between RNA biology and protein-modification pathways. Our study confirms and expands the atlas of RBPs, providing a useful resource for the study of the RNA-RBP network in stem cells.
Project description:Embryonic stem cell (ESC) self-renewal and cell-fate decisions are driven by a broad array of molecular signals. While transcriptional regulators have been extensively studied in human ESCs (hESCs), the extent to which RNA-binding proteins (RBPs) contribute to human pluripotency remains unclear. Here, we carried out a proteome-wide screen and identified 810 proteins that directly bind RNA in hESCs. We determined the RBP catalog by using RNA-interactome capture (RIC), a method based on UV light-mediated cross-linking (CL) of RNAs to proteins in living cells, followed by oligo(dT) purification of poly(A)-RNA-protein complexes and mass spectrometry analysis of captured proteins. As control, we applied a similar strategy to non-cross-linked (non-CL) samples. To uncover the identity of the eluted proteins, we performed in-solution tryptic digestion of CL and non-CL eluates and analyzed their contents by a high-resolution mass spectrometer (Q-Exactive Plus). We then performed differential proteome analysis between CL and non-CL eluates, resulting in a set of 810 high-confidence protein groups, defined as the hESC RNA-interactome. RIC was carried out in four independent biological replicates. This data accompanies the manuscript: "Uncovering the RNA-binding protein landscape in the pluripotency network of human embryonic stem cells".
Project description:RNA-binding proteins (RPBs) are deeply involved in many fundamental cellular processes in bacteria and are vital for their survival. Despite this, few studies have so far been dedicated to globally identifying bacterial RBPs. We have adapted the RNA interactome capture (RIC) technique, originally developed for eukaryotic systems, to globally identify RBPs in bacteria. RIC takes advantage of the base pairing potential of poly(A) tails to pull-down mRNA-protein complexes. By overexpressing the poly(A) polymerase I, we drastically increase the frequency of polyadenylated RNA in E. coli, allowing us to pull down RNA-protein complexes using immobilized oligo-d(T) as bait. With this approach, we identified 167 putative RBPs, roughly half of which are already annotated as RNA-binding. We experimentally verified the RNA-binding ability of several proteins previously unknown to interact with RNA, including the uncharacterized protein YhgF. YhgF is exceptionally well conserved not only in bacteria, but also in archaea and eukaryotes. We identified YhgF in vivo RNA targets using CLIP-seq, two of which were verified using electromobility shift assays. Our findings present a simple and robust strategy for RBP identification in bacteria, provide a resource of new bacterial RBPs, and lays the foundation for further studies of the strongly conserved RBP Yhg
Project description:Mammalian chromosomes are partitioned into topologically associating domains (TADs) by the loop-extrusion activity of cohesin that is blocked at specific DNA sites bound by CTCF. Chromosome structure inside TADs is highly variable in single cells, yet little is known about its temporal dynamics, how it influences the rates and durations of chromosomal contacts, and how it depends on CTCF and cohesin. To address these questions we combine two quantitative live-cell imaging strategies that minimize locus-specific confounding effects. We show that loop extrusion by cohesin globally reduces the mobility of the chromatin fiber in living cells, while also increasing the rates of formation and durations of contacts between sequences inside the same TAD. Quantitative analysis of high-resolution microscopy data reveals that contacts assemble and disassemble frequently in the course of the cell cycle, and become substantially more frequent and longer in the presence of convergent CTCF sites. Comparison with polymer modeling additionally reveals that cohesin-mediated CTCF loops last around 10 minutes on average. Our data support the notion that chromosome structure within TADs is highly dynamic and provide a quantitative framework for understanding the principles that link chromosome structure to biological function.
Project description:We conducted UV cross-linking immunoprecipitation (CLIP) with and without phosphatase inhibitor and compared the outcome. The topmost band on the western blots appeared more prominent with the inhibitor. The RNA-binding activity of the band was also stronger with the inhibitor. We isolated the band and subjected to LC-MS/MS to identify the phosphorylated residues.