High-Precision ChIRP-MS Service: Unbiased Mapping of Endogenous RNA-Protein Interactions

Discover the true physiological interactome of your target RNA. Our high-resolution ChIRP-MS service utilizes in vivo cross-linking and custom split-pool probe design to capture endogenous RNA-protein complexes with maximum specificity. From probe synthesis to advanced bioinformatics, we deliver publication-ready proteomic insights for lncRNA, circRNA, mRNA, and viral RNA research, effectively eliminating the false positives commonly associated with traditional in vitro methods.

Endogenous Detection: Capture authentic interactions in their native physiological state without the artifacts of genetic over-expression.
Zero-Background Confidence: Dual-probe split-pool strategy strictly filters out non-specific binding.
High-Resolution Precision: Powered by industry-leading Orbitrap LC-MS/MS instrumentation.
Multi-Omic Versatility: Foundation for studying RNA-DNA and RNA-RNA associations alongside proteomics.

Consult Our Technical Experts

What is ChIRP-MS? Principle of Endogenous RNA-Protein Interaction Mapping

ChIRP-MS (Chromatin Isolation by RNA Purification followed by Mass Spectrometry), a core technique within our comprehensive ChIRP Service platform, is a robust RNA-centric proteomic assay. It utilizes a tiling array of biotinylated DNA probes to selectively capture specific endogenous RNA transcripts along with their interacting protein complexes from cross-linked cells, followed by precise LC-MS/MS identification.

Unlike traditional methods that rely on single synthetic probes or in vitro transcribed RNA baits, ChIRP-MS employs a multi-probe strategy hybridized across the entire length of the target RNA. By cross-linking the cells prior to lysis, the assay "freezes" both stable and transient interactions. Furthermore, because the ChIRP method effectively enriches the entire genomic and transcriptomic context associated with the target RNA, it can be adapted to map lncRNA-DNA interactions (ChIRP-DNA-seq/PCR) and lncRNA-RNA interactions (ChIRP-RNA-seq/PCR), offering a complete spatial map of RNA associations.

Overcoming Challenges in RNA-Protein Interactome Discovery

Identifying the functional proteomic scaffold of non-coding RNAs is notoriously difficult. Our service directly addresses the three major roadblocks researchers face when mapping interactomes:

The In Vitro Folding Artifact: Traditional pull-down assays often use in vitro transcribed RNA, which may not fold into its native secondary or tertiary structure, leading to biologically irrelevant protein binding.
High False-Positive Rates: Magnetic beads and single-probe systems are prone to non-specific background noise, often capturing highly abundant structural proteins or ribosomal subunits that mask true interactors.
The Low-Abundance Challenge: Many regulatory lncRNAs or enhancer RNAs are expressed at extremely low copies per cell, making their associated protein complexes nearly impossible to detect with standard sensitivity thresholds.

Technical Advantages of Our Custom ChIRP-MS Service

To overcome these challenges and ensure data reliability, our service incorporates rigorous biochemical innovations:

Split-Pool (Odd/Even) Probe Strategy

We design up to 50 distinct tiling probes against your target RNA and divide them into two independent pools (Odd and Even). True interactors must be significantly enriched in both independent captures, effectively mathematically eliminating random background noise.

Endogenous In Vivo Cross-linking

We utilize optimized glutaraldehyde or formaldehyde cross-linking protocols to preserve precise stoichiometry, capturing physiological interactions right at the chromatin or cytoplasmic level.

RNase-Treated Negative Controls

By running parallel samples treated with RNase prior to capture, we definitively prove that the isolated proteins are dependent on the presence of the target RNA, not DNA or bead matrix affinity.

Technical Services

Service Scope Workflow Platform Bioinformatics Case Study Deliverables Sample Requirements Tech Comparison FAQ Get a Custom Proposal

ChIRP-MS Service Scope: Target RNA Species & Interactome Applications

Long Non-Coding RNAs (lncRNAs)

Discovering chromatin-modifying enzymes and transcriptional co-activators mapped to specific genomic loci to understand epigenetic regulation.

Circular RNAs (circRNAs)

Identifying RNA-binding proteins (RBPs) that interact with back-spliced junctions or profiling the "protein-sponge" function of mature circRNAs.

Messenger RNAs (mRNAs)

Investigating the protein-binding landscape of protein-coding transcripts to study mRNA stability, localization, and translational control.

Viral RNAs & Enhancer RNAs

Uncovering how viral genomes hijack host cellular machinery and mapping architectural proteins involved in enhancer-promoter looping.

ChIRP-MS Workflow & Quality Control (QC) Checkpoints

Reliable MS data relies on flawless sample preparation. Our end-to-end workflow is governed by strict Quality Control (QC) gates at every critical transition.

End-to-end ChIRP-MS workflow diagram illustrating in vivo cross-linking, RNA-probe hybridization, bead capture, and MS detection.

Custom Probe Design & Synthesis

Tiling probes are algorithmically designed to avoid off-target genomic or transcriptomic binding, followed by high-purity biotinylation.

Cross-linking & Cell Lysis

Samples undergo controlled cross-linking and optimized sonication to shear chromatin into ideal lengths.

QC Checkpoint 1: Sonication efficiency profiling via agarose gel or Bioanalyzer.

Hybridization & Bead Capture

Target RNA is hybridized with the Odd and Even probe pools and captured via high-affinity streptavidin beads.

QC Checkpoint 2: RT-qPCR quantification to ensure >70% target RNA recovery from the lysate.

Stringent Washing & Elution

Proprietary buffer systems wash away non-specific binders before proteins are eluted.

QC Checkpoint 3: RNase control validation to confirm target specificity.

Trypsin Digestion & Peptide Cleanup

Proteins are digested into peptides and desalted.

QC Checkpoint 4: Peptide concentration and quality assessment prior to injection.

High-Resolution LC-MS/MS

Peptides are analyzed utilizing our advanced mass spectrometry platforms.

QC Checkpoint 5: System calibration and MS1/MS2 quality metrics review.

Advanced LC-MS/MS Instrumentation for RNA-Directed Proteomics

The depth of your interactome discovery is directly tied to the sensitivity of the mass spectrometer. Our analytical facility is equipped with industry-leading technology to ensure maximum coverage.

To guarantee the detection of ultra-low abundance regulatory proteins, we utilize Thermo Scientific™ Orbitrap Exploris™ 480 and Fusion™ Lumos™ Tribrid™ systems. Our platform also supports the identification of protein isoforms and post-translational modifications (PTMs). By capturing RNAs in their physiological cross-linked state, ChIRP-MS allows researchers to visualize not only which proteins are bound but also their specific modification states, providing deeper insights into the regulation of endogenous RNP complexes.

Key Mass Spectrometry Parameters for ChIRP-MS:

Parameter	Specification (Orbitrap Exploris / Lumos)	Benefit for ChIRP-MS Discovery
Mass Resolution	Up to 480,000 (FWHM) at m/z 200	Unambiguous peptide identification, effectively resolving isobaric overlaps in complex RNP mixtures.
Mass Accuracy	< 1 ppm (with internal calibration)	Ensures high-confidence RBP identification with exact mass mapping.
Sensitivity	Sub-femtomole to attomole level	Unlocks the ability to detect trace-level transcription factors and transient chromatin modifiers.
Scan Rate	Up to 40 Hz	Maximizes MS/MS spectra acquisition, preventing the loss of low-abundance signals.
Quantification	Label-Free Quantification (LFQ)	Provides accurate relative abundance of proteins across the Odd/Even probe pools.

Orbitrap Fusion Lumos Tribrid Mass Spectrometer for high-resolution ChIRP-MS analysis

Orbitrap Fusion Lumos Tribrid System

Comprehensive Bioinformatics Analysis for RNP Complexes

Mass spectrometry generates complex datasets. Our bioinformatics team bridges the gap between raw spectra and biological interpretation, offering scalable analysis packages tailored to your project.

Standard Analysis Pipeline:

Data Pre-processing & QC: Spectral counting, LFQ intensity normalization, and replicate correlation analysis.
Protein Identification & Filtering: Database searching using MaxQuant or Proteome Discoverer, filtered strictly by FDR < 1%.

Advanced Bioinformatics Add-ons:

Differential Enrichment Analysis: Statistical comparison across multiple biological conditions (e.g., wild-type vs. mutant).
GO/KEGG Pathway Enrichment: Profiling the functional pathways associated with your identified RNP interactome.
PPI Network Visualization: Mapping the architectural structure of the complex using STRING and Cytoscape.
Domain Analysis: Identifying enriched RNA-Binding Domains (RBDs) among the captured interactors.

Case Study

Profiling the Xist lncRNA Interactome

Research Objective:

To comprehensively identify the endogenous protein interactors of Xist, a long non-coding RNA responsible for X-chromosome inactivation, in native chromatin contexts without genetic manipulation.

How ChIRP-MS Was Used:

Method: ChIRP-MS was applied using a tiling array of biotinylated oligonucleotides, separated into Odd and Even pools, against Xist RNA in cross-linked mouse embryonic stem cells (mESCs).
Conditions: 1% Glutaraldehyde cross-linking, RNase A/H elution controls, and high-resolution LC-MS/MS quantification.

Key Findings from ChIRP-MS:

Identified 81 high-confidence Xist-interacting proteins that were highly enriched in both the Odd and Even probe sets compared to controls.
Discovered that Xist directly interacts with SPEN (SHARP), hnRNP K, and LBR.
Confirmed that SPEN is an essential co-factor required for Xist-mediated gene silencing.

Why ChIRP-MS Was Essential:

Enabled unbiased discovery of the RNP complex in its native, in vivo cross-linked state.
Eliminated the high background noise typical of in vitro pull-downs by requiring strict overlap between two independent probe pools.

Reference

Chu, C., et al. "ChIRP-MS: RNA-directed proteomic purification of RNA-protein complexes." Nature Methods 12.4 (2015): 335-337. https://doi.org/10.1038/nmeth.3321

ChIRP-MS identification of Xist lncRNA interacting proteins

High-confidence Xist-interacting proteins (e.g., SPEN, hnRNP K) identified by overlapping Odd and Even probe pools in ChIRP-MS.

ChIRP-MS Project Deliverables & Publication-Ready Demo Results

Your final data package is engineered to support seamless integration into your research narrative, grant applications, and high-impact journal submissions.

Standard File Deliverables:

Comprehensive Project Report: Detailed methodology suitable for your manuscript's "Materials & Methods" section, along with QC profiles (sonication and qPCR capture efficiency).
Protein Identification Datasets: High-confidence interactor lists (Excel/CSV) strictly filtered by False Discovery Rate (FDR < 1%) and Odd/Even probe overlap.
Raw Spectra Data: Original mass spectrometry .RAW files and standard search engine outputs for your institutional repository requirements.

Publication-Ready Visualizations (Demo Results):

To provide absolute confidence in our ChIRP-MS service, our bioinformatic pipeline delivers the following critical visualizations, proving both the specificity of the capture and the biological relevance of your RNA's interactome.

RT-qPCR bar chart demonstrating high target RNA capture efficiency and specificity against RNase controls in a ChIRP-MS assay.

1. Target RNA Capture Efficiency (RT-qPCR)

Target RNA enrichment validation via RT-qPCR compared to RNase controls. Before proceeding to mass spectrometry, we rigorously prove the physical capture was successful.

Venn diagram showing high-confidence RNA-binding proteins identified by overlapping Odd and Even probe pools in ChIRP-MS.

2. Specificity Filtering via Split-Pool Strategy

High-confidence RBP identification through Odd/Even split-pool probe overlap. Proteins appearing in the intersection are classified as high-confidence interactors.

Bubble plot visualization of Gene Ontology and KEGG pathway enrichment analysis for endogenous RNA-protein interactions.

3. Biological Pathway Enrichment

GO and KEGG pathway enrichment mapping of the identified RNP interactome. Visualizations categorize the identified proteins, revealing functional clusters.

Protein-protein interaction network diagram illustrating the core ribonucleoprotein complex architecture mapped by ChIRP-MS.

4. Protein-Protein Interaction (PPI) Network Mapping

PPI network modeling of the target RNA's proteomic scaffold and core complexes, highlighting "hub" proteins and architectural structure.

ChIRP-MS Sample Requirements & Cell Cross-linking Guidelines

Proper sample preparation is critical for maintaining in vivo interactions. Please refer to our minimum guidelines below.

Sample Type	Minimum Input	Recommended Input	Preparation & Fixation	Shipping Condition
Adherent Cells	2 × 10⁷ cells	5 × 10⁷ cells	1% Glutaraldehyde / Formaldehyde cross-linked	Dry Ice
Suspension Cells	3 × 10⁷ cells	6 × 10⁷ cells	1% Glutaraldehyde / Formaldehyde cross-linked	Dry Ice
Animal Tissues	200 mg	500 mg	Flash-frozen, homogenized & cross-linked	Dry Ice
Clinical Biopsies	Consult Team	Consult Team	Specialized low-input fixation required	Dry Ice

*Note: For extremely low-abundance lncRNAs, we may recommend scaling up the starting material. Please consult our technical team before initiating cross-linking.

ChIRP-MS vs. Alternative Technologies: Selecting the Right Assay

Selecting the appropriate RNA-protein interaction strategy depends entirely on your scientific question and the biological materials available.

Technology Comparison Table

Dimension	ChIRP-MS	RIP-MS / RIP-seq	RNA Pull-down	Co-IP	RIME-MS
Target Focus	RNA-Centric (Known RNA)	Protein-Centric (Known Protein)	RNA-Centric (Known RNA)	Protein-Centric (Known Protein)	Protein-Centric (Known Chromatin Protein)
Binding Environment	In Vivo (Endogenous)	In Vivo (Endogenous)	In Vitro (Cell Lysate)	Native / Cell Lysate	Cross-linked Chromatin
Primary Advantage	High physiological relevance; discovers novel RBPs.	Excellent for mapping known RBP targets globally.	Simple workflow; rapid validation.	Validates known endogenous protein-protein interactions.	Identifies chromatin complex co-factors & TFs.
Probe/Bait Type	Tiling DNA probes (Split-pool)	Specific Protein Antibody	In vitro transcribed RNA bait	Specific Protein Antibody	Specific Protein Antibody
False Positive Rate	Very Low (due to strict dual-probe filtering)	Low	High (prone to non-specific folding artifacts)	Medium/Variable	Low (controlled via cross-linking)

Solution Selection Guide

Choose ChIRP-MS if: You have discovered a novel lncRNA or circRNA and need to map its unknown proteomic partners exactly as they interact inside the living cell, without over-expression artifacts.
Choose RIP-seq / RIP-MS if: You are focusing on a specific, known RNA-binding protein (e.g., Argonaute, EZH2) and want to discover all the RNA transcripts it regulates globally. Learn more about our RIP-seq Service.
Choose CLIP-seq if: You know the interacting RBP but need to identify the exact, single-nucleotide resolution binding sites on the RNA. Explore our CLIP-seq Service.
Choose RNA Pull-down if: You need a rapid, cost-effective method to validate a direct physical interaction using synthesized RNA motifs, and absolute in vivo context is not strictly required. Explore our RNA Pull-down Service.

FAQs for ChIRP-MS and RNA-Protein Interaction Services

How long should the target RNA be for a successful ChIRP-MS assay?

A. Ideally, the target RNA should be longer than 500 nucleotides to accommodate a robust tiling probe design (typically 20–50 distinct probes). For shorter RNAs (e.g., mature miRNAs or short circRNAs), specialized single-probe captures or alternative cross-linking strategies may be required.

How do you differentiate between direct RNA-protein interactions and indirect complex associations?

A. Because ChIRP utilizes glutaraldehyde or formaldehyde cross-linking, it captures the entire intact chromatin or RNP complex. Therefore, the resulting MS data will include both direct RNA-binding proteins (RBPs) and secondary associated proteins (e.g., structural scaffold proteins). To pinpoint direct binding sites, supplementary orthogonal assays like CLIP-seq may be recommended.

What if my cell input does not meet the recommended requirements?

A. For rare cell populations or clinical samples, we employ optimized low-input protocols utilizing enhanced micro-chromatin fragmentation and highly sensitive Orbitrap detection. However, lower input may affect the detection limits of low-abundance interactors. Please consult our team for a feasibility assessment.

Do you provide custom probe design, and is it included in the service?

A. Yes. Our bioinformaticians custom design the complete tiling probe library, meticulously evaluating thermodynamics and avoiding off-target genomic alignments. The synthesis of high-purity biotinylated probes is fully included in our standard ChIRP-MS workflow.

What is the difference between ChIRP-MS, RAP-MS, and CHART-MS?

A. All three are RNA-centric purification methods capturing in vivo cross-linked complexes. The primary differences lie in probe chemistry and elution. ChIRP uses shorter tiling DNA probes and glutaraldehyde, making it highly robust and broadly applicable. RAP uses long antisense RNA probes, and CHART uses RNase H-based specific elution. ChIRP is generally considered the most versatile and rigorously validated for mass spectrometry analysis.

Can ChIRP-MS be used to discover RNA-RNA interactions?

A. Standard ChIRP-MS is optimized for identifying RNA-protein interactions via mass spectrometry. While co-precipitated RNAs can technically be sequenced (explore our ChIRP-seq Service) to identify RNA-RNA or RNA-DNA associations, this requires a distinct genomic/transcriptomic sequencing pipeline rather than proteomics.