Crosslinking-Immunoprecipitation (CLIP) Service

Crosslinking-immunoprecipitation (CLIP) is a high-resolution technique designed to map the precise binding sites of RNA-binding proteins (RBPs) on their target RNAs at nucleotide-level resolution. By utilizing in vivo UV crosslinking to covalently "freeze" direct protein-RNA contacts, CLIP minimizes background from indirect associations. At CD BioSciences, we offer comprehensive CLIP services, from validating specific binding sites to genome-wide discovery of RBP-RNA interactions. Our optimized protocols, rigorous controls, and advanced sequencing/bioinformatics pipeline deliver high-confidence, publication-ready data to decipher the precise regulatory code of RBPs.

Mechanism of Crosslinking-Immunoprecipitation (CLIP)

Crosslinking-Immunoprecipitation is a pivotal technique for identifying the exact genomic locations where an RNA-binding protein (RBP) directly contacts RNA. Its core mechanism involves brief in vivo UV irradiation of cells, which creates covalent bonds between the RBP and its directly bound RNA nucleotides, effectively "capturing" momentary interactions. Following cell lysis, the target RBP and its crosslinked RNA are specifically co-immunoprecipitated. After stringent washing and RNA-protein complex purification, the bound RNA fragments are isolated, sequenced, and mapped back to the genome, revealing the protein's binding motifs and sites.

Fig.1 RNA-Protein Crosslinking and Immunoprecipitation Sequencing (CLIP-seq) Flowchart. (Rosenberg M, et al., 2021)

Applications of Crosslinking-Immunoprecipitation (CLIP) Technology

The principal advantage and significance of CLIP lie in its high resolution and specificity for direct interactions. Unlike native methods, UV crosslinking captures transient yet direct contacts, allowing for precise mapping of binding sites, which is essential for understanding regulatory mechanisms like splicing, stability, and translation control. This makes it the gold-standard technique for:

1. Defining the exact binding landscape and consensus motifs of an RBP.
2. Distinguishing direct regulators from indirect complex members in regulatory networks.
3. Identifying disease-driving mutations that alter RBP binding specificity or affinity.
4. Validating and refining computational predictions of RBP binding sites.

Our Services

Nucleotide-resolution mapping presents unique challenges: optimizing crosslinking efficiency, handling picogram amounts of crosslinked RNA, and applying specialized bioinformatics to distinguish signal from noise. Our service is engineered to master these steps. We employ calibrated UV crosslinking, stringent denaturing purification, and optimized library construction protocols for short, crosslinked fragments (including iCLIP and eCLIP adaptations). From experimental design to advanced peak calling, CD BioSciences ensures your data meets the highest standards of reliability.

Our CLIP Service Portfolio

Genome-Wide CLIP-Seq Service

For discovery-phase research, our CLIP-Seq service provides a genome-wide, high-resolution map of all direct RNA binding sites for your RBP of interest. Following immunoprecipitation and size selection, the recovered RNA-protein complexes are used to construct sequencing libraries specifically tailored for CLIP-derived material (such as iCLIP or eCLIP adaptations). High-throughput sequencing and sophisticated bioinformatics analysis then identify significantly enriched peaks, revealing binding sites, motifs, and target transcripts. This approach is powerful for discovering novel binding sites, defining sequence/structural preferences, and understanding the global regulatory network of an RBP.

Standard CLIP-qPCR Service

This service is ideal for validating suspected binding sites identified from CLIP-Seq data or other sources, or for quantifying changes in RBP binding at specific genomic loci under different conditions. We use your specified, validated antibodies to immunoprecipitate the UV-crosslinked RBP-RNA complexes. After rigorous processing, the co-precipitated RNA is purified and analyzed via quantitative RT-PCR using primers designed for your regions of interest. This service delivers precise, quantitative data on protein occupancy at specific sites, perfect for focused mechanistic studies.

Sample Requirements & Experimental Design

We are flexible and can work with various sample types, including cultured cell lines (adherent or suspension). A key requirement is that samples must be amenable to in vivo UV crosslinking. During project consultation, our experts will work with you to determine the optimal cell number based on your RBP's abundance and the chosen method (qPCR vs. Seq). The use of a high-quality, validated antibody for the target RBP is critical. We can source the antibody or use a client-provided antibody, subject to validation. We also assist in designing essential experimental controls.

Samples and Applications

Supported Sample Types

1. UV-Crosslinked Cell Cultures. Adherent or suspension mammalian cell lines, pretreated and prepared for optimal in vivo UV crosslinking to capture native interactions.
2. Perturbed or Engineered Systems. Cells subjected to drug treatments, genetic knockdown/overexpression, or environmental stressors. Cells expressing epitope-tagged RBPs (e.g., FLAG, HA) for reliable immunopurification are also supported.

Diverse Application Scenarios

1. Nucleotide-Resolution Mapping. Pinpoint the exact genomic locations where an RNA-binding protein contacts its RNA targets.
2. Regulatory Mechanism Elucidation. Decipher how binding at specific sites controls RNA splicing, stability, or translation.
3. Disease Mutation Analysis. Determine how disease-associated mutations alter a protein's RNA-binding specificity or function.
4. Drug Target Validation. Confirm whether a therapeutic compound successfully disrupts the intended protein-RNA interaction.
5. Dynamic Network Profiling. Compare binding landscapes across conditions to reveal how cellular signals rewire RNA-protein networks.

Our CLIP Workflow

Our proven, five-step pipeline ensures robust and reproducible capture of direct protein-RNA interactions.

Project Design & Consultation

We collaborate with you to define the project scope, including target protein, cell type, desired readout (qPCR or Seq), and necessary controls (e.g., IgG control, size-matched input RNA).

In Vivo & Complex Isolationn

Your cells undergo optimized UV crosslinking. We then lyse cells under denaturing conditions and perform immunoprecipitation with stringent washes to purify only the covalently linked RBP-RNA complexes.

RNA Processing & Library Prep

The complex is treated with RNase to trim away unbound RNA, leaving only the protected, crosslinked fragment. RNA is isolated, and for CLIP-seq, converted into a sequencing-compatible library.

High-Resolution Analysis

Samples are analyzed via CLIP-qPCR or sequenced. Our bioinformatics pipeline for CLIP-seq includes adapter trimming, alignment, sophisticated peak calling, motif discovery, and functional annotation.

Comprehensive Reporting & Delivery

You receive a detailed report with all protocols, QC metrics, raw data files (e.g., BAM, BED), analyzed results (peak files, motif logos), and a clear interpretation of the biological findings.

Why Choose Us?

1. High-Resolution Mapping. Our optimized UV crosslinking and RNase trimming steps enable the identification of direct protein-RNA interaction sites at nucleotide-level resolution.
2. Superior Signal-to-Noise Ratio. Denaturing IP conditions and stringent washes minimize indirect associations, ensuring the identified binding sites are direct and specific.
3. Platform-Specific Expertise. We employ library preparation methods tailored for short, crosslinked RNA fragments (e.g., iCLIP/eCLIP protocols), maximizing data quality and unique mapping rates.
4. Advanced Bioinformatics. Our dedicated CLIP-seq analysis pipeline includes sophisticated peak calling, motif analysis, and integration with RNA-seq or annotation databases to derive biological insights.

Frequently Asked Questions (FAQs)

CD BioSciences' Crosslinking-Immunoprecipitation (CLIP) Service provides the definitive solution for researchers requiring nucleotide-level precision in RNA-protein interaction studies. By capturing direct, in vivo binding events, our service moves beyond association to reveal the exact regulatory grammar of your RNA-binding protein. From discovering novel binding motifs and validating drug targets to elucidating disease mechanisms, we deliver the high-resolution, publication-ready data needed to advance your most challenging research questions. Contact us to map the precise interactions that govern post-transcriptional control.

Reference

1. Rosenberg M, Levy V, Maier V K, et al. Denaturing cross-linking immunoprecipitation to identify footprints for RNA-binding proteins[J]. STAR protocols, 2021, 2(4).