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Chromatin Immunoprecipitation (ChIP) Protocol
Use this guided ChIP protocol page to choose a cross-linking ChIP, native ChIP, ChIP-qPCR, or ChIP-seq preparation workflow. The steps below are practical starting conditions for antibody-based enrichment of chromatin-associated DNA. Optimize fixation, fragmentation, antibody amount, bead type, wash stringency, and downstream detection for each target and sample type.
For kit-supported workflows, choose a ChIP enrichment kit, qPCR reagent, or ChIP-seq library preparation kit that matches your starting material, input amount, and downstream readout.
Typical starting inputs
- Histone marks: 1 x 105 to 1 x 106 cells per IP may be sufficient after optimization.
- Transcription factors: start with 1 x 106 to 1 x 107 cells per IP.
- Low-abundance cofactors: use higher input, stronger controls, and replicate IPs.
Cross-linking ChIP protocol
Use cross-linking ChIP for transcription factors, cofactors, chromatin regulators, and many DNA-associated proteins that may not remain bound during native extraction.
- Use this format when: The target is a non-histone protein, a weak or transient DNA-binding factor, or a chromatin complex that benefits from formaldehyde stabilization.
- Relevant ChIP kits: For standard mammalian cell ChIP, see the EpiQuik Chromatin Immunoprecipitation (ChIP) Kit. For low-input or high-sensitivity ChIP from cells or tissues, see the ChromaFlash High-Sensitivity ChIP Kit.
- Optimize first: Crosslinking time, sonication conditions, antibody amount, bead type, wash stringency, and qPCR primer performance.
1
Prepare cells and fresh buffers
Start with 1 x 106 to 1 x 107 cells per IP. Chill PBS, wash buffers, and collection tubes. Add fresh protease inhibitors to all lysis and wash buffers immediately before use.
2
Crosslink protein-DNA complexes
Add formaldehyde directly to culture medium to 1 percent final concentration. Incubate 10 minutes at room temperature with gentle rocking. For sensitive epitopes, test 5, 8, and 10 minutes in a pilot experiment.
3
Quench crosslinking
Add glycine to 125 mM final concentration and incubate 5 minutes at room temperature. Aspirate medium and wash cells 2-3 times with cold PBS containing protease inhibitors.
4
Collect and lyse cells
Scrape adherent cells in 1 mL cold PBS per 10 cm dish or pellet suspension cells at 500 x g for 5 minutes at 4°C. Resuspend the pellet in ChIP lysis buffer at about 1 mL per 1 x 107 cells. Incubate 10-15 minutes on ice.
5
Fragment chromatin
Sonicate on ice or in a cooled sonication system to a starting DNA size of 200-800 bp for ChIP-qPCR or 150-500 bp for many ChIP-seq workflows. Keep samples cold and avoid foaming. Clarify at 12,000 x g for 10 minutes at 4°C.
6
Check fragmentation and save input
Remove 20-50 uL sheared chromatin for reversal and gel or Bioanalyzer check. Save 1-10 percent input chromatin before antibody addition. Store input at 4°C overnight or at -20°C if processing later.
7
Pre-clear chromatin
Pre-clear chromatin with 20-40 uL blocked protein A/G magnetic beads for 30-60 minutes at 4°C with rotation. Transfer the supernatant to a new tube and avoid carrying over beads.
8
Add ChIP antibody
Add 2-5 ug primary antibody per IP as a starting range. For low-abundance targets, test 5-10 ug or more chromatin. Include IgG control and a known positive ChIP antibody when available. Rotate overnight at 4°C.
9
Capture immune complexes
Add 30-50 uL washed, blocked protein A/G magnetic beads. Rotate 2-4 hours at 4°C. Place tubes on a magnetic stand and remove unbound supernatant.
10
Wash beads sequentially
Wash beads with 1 mL cold buffer per wash. Use 2 washes low-salt buffer, 2 washes high-salt buffer, 1 wash LiCl buffer, and 2 washes TE buffer as a stringent starting sequence. Rotate 3-5 minutes per wash unless the target is fragile.
11
Elute and reverse crosslinks
Elute twice with 100-120 uL elution buffer per elution at room temperature for 10-15 minutes. Combine eluates. Add NaCl to 200 mM final concentration and reverse crosslinks at 65°C for 4 hours to overnight. Treat with RNase A and proteinase K before DNA purification.
12
Purify and analyze DNA
Purify DNA using a spin-column, magnetic bead, or phenol/chloroform cleanup method compatible with low DNA input. Elute in 30-50 uL low-EDTA TE or nuclease-free water. Analyze enrichment by qPCR or proceed to sequencing library preparation.
Fragment sizeLarge fragments can reduce resolution. Over-shearing can reduce recovery or damage epitopes. Always verify shearing before interpreting poor enrichment.
CrosslinkingOver-crosslinking can mask epitopes and lower antibody capture. Under-crosslinking can lose weakly bound targets.
Native ChIP protocol
Use native ChIP for histones and many histone modifications when preserving native nucleosome structure is preferred and formaldehyde crosslinking is not required.
- Use this format when: The target is a histone protein or histone modification with strong chromatin association.
- Optimize first: MNase digestion, nucleosome fragment range, antibody amount, and salt conditions during immunoprecipitation.
1
Collect cells without crosslinking
Start with 1 x 106 to 5 x 106 cells per IP for histone targets as a practical starting range. Wash cells twice with cold PBS and keep all steps cold unless digestion conditions require warmth.
2
Prepare nuclei
Resuspend the cell pellet in hypotonic or nuclear isolation buffer containing protease inhibitors. Incubate on ice 10 minutes. Dounce gently if needed. Pellet nuclei at 800-1,000 x g for 5 minutes at 4°C.
3
Digest chromatin with MNase
Resuspend nuclei in MNase digestion buffer containing calcium. Add a titrated amount of micrococcal nuclease and incubate at 37°C for 5-20 minutes. Start with a small pilot digestion to identify conditions that produce mostly mono- and oligonucleosomes.
4
Stop digestion
Add EDTA to 5-10 mM final concentration to stop MNase activity. Place samples on ice immediately. Avoid prolonged digestion after the stop step.
5
Release soluble chromatin
Lyse nuclei gently with native ChIP lysis or IP buffer containing 0.1-0.5 percent NP-40 or Triton X-100 and physiological salt. Incubate on ice 10 minutes, then clarify at 12,000 x g for 10 minutes at 4°C.
6
Check nucleosome size and save input
Remove 20-50 uL chromatin for DNA purification and size check. A useful native ChIP digestion often includes mono-, di-, and tri-nucleosome DNA with a major range around 150-600 bp. Save 1-10 percent input.
7
Pre-clear chromatin
Incubate chromatin with 20-40 uL blocked protein A/G beads for 30-60 minutes at 4°C with rotation. Transfer the pre-cleared supernatant to a new tube.
8
Add histone or PTM antibody
Add 1-5 ug primary antibody per IP as a starting range. For abundant histone marks, lower antibody and lower chromatin input may be sufficient. Rotate 2-4 hours or overnight at 4°C.
9
Capture with beads
Add 30-50 uL washed, blocked protein A/G beads and rotate 1-2 hours at 4°C. Use magnetic separation or low-speed spin collection depending on bead type.
10
Wash under native conditions
Wash 4-6 times with cold native ChIP wash buffer. Start with 1 mL per wash and 3-5 minutes rotation. Increase salt or detergent only if background is high and recovery remains acceptable.
11
Elute DNA-protein complexes
Elute with 100-200 uL elution buffer compatible with DNA recovery, commonly SDS-containing elution buffer or proteinase K digestion buffer. Treat with proteinase K at 55-65°C for 1-2 hours.
12
Purify DNA and quantify enrichment
Purify DNA and elute in 30-50 uL. Analyze by qPCR using input-normalized percent input or fold enrichment over IgG. For sequencing, confirm DNA yield and library compatibility before pooling samples.
Best fitNative ChIP is usually strongest for histone marks and may not preserve weak or transient transcription factor binding.
MNase titrationMNase digestion is sample dependent. Always optimize enzyme amount and digestion time before large experiments.
ChIP-qPCR analysis protocol
Use ChIP-qPCR to validate enrichment at defined genomic loci after native or cross-linking ChIP.
- Use this format when: Testing a known locus, validating ChIP enrichment, optimizing a new ChIP antibody, or confirming ChIP-seq findings.
- Relevant ChIP-qPCR kits: Pair ChIP-enriched DNA with the EpiQuik Quantitative PCR Fast Kit for fast quantitative real-time PCR analysis of ChIP DNA. Use a ChIP enrichment kit such as EpiQuik ChIP Kit or ChromaFlash High-Sensitivity ChIP Kit upstream.
- Optimize first: Primer specificity, amplicon size, qPCR efficiency, positive and negative loci, input dilution, and replicate consistency.
1
Design ChIP-qPCR primers
Design primers for 70-150 bp amplicons centered on the expected binding or modification region. Include at least one positive locus and one negative locus when possible.
2
Validate primer efficiency
Test primers on input DNA dilution series. Aim for a single melt peak and similar amplification efficiency across primer sets. Redesign primers if primer dimers or non-specific products appear.
3
Dilute ChIP and input DNA
Use 1-2 uL purified ChIP DNA per 10-20 uL qPCR reaction as a starting point. Dilute input DNA so Ct values fall in the linear range and are not several cycles earlier than the ChIP samples.
4
Set up qPCR reactions
For each 20 uL reaction, combine 10 uL 2x qPCR master mix, primer mix at validated concentration, 1-2 uL DNA, and nuclease-free water. The EpiQuik Quantitative PCR Fast Kit can be used for ChIP DNA qPCR analysis. Run technical duplicates or triplicates for input, target IP, IgG IP, and controls.
5
Use consistent controls
Include no-template controls, input DNA, IgG IP DNA, positive control IP DNA when available, and negative genomic loci. If using primary antibody for a new target, include a known responsive biological condition when possible.
6
Calculate percent input
Correct input Ct for dilution, then calculate percent input for each IP. A common formula is 100 x 2^(adjusted input Ct - IP Ct). Apply the same formula to target IP and IgG IP.
7
Calculate fold enrichment
Calculate enrichment over IgG or over a negative locus when appropriate. Report the normalization method clearly because percent input and fold enrichment answer different questions.
8
Interpret enrichment with controls
A useful ChIP-qPCR result should show enrichment at expected loci, low IgG background, acceptable input amplification, and reproducibility across biological replicates. Weak signal at all loci usually points to chromatin, antibody, or wash stringency issues.
Amplicon sizeShort amplicons perform better with fragmented ChIP DNA. Long amplicons can underperform after heavy shearing.
Negative lociNegative loci help distinguish real locus-specific enrichment from antibody or bead background.
ChIP-seq preparation and QC protocol
Use this workflow after native or cross-linking ChIP when the enriched DNA will be used for sequencing library preparation.
- Use this format when: ChIP DNA will be converted into sequencing libraries for genome-wide mapping.
- Relevant ChIP-seq kit: For an all-in-one ChIP and ChIP-seq library preparation workflow, see the EpiNext ChIP-Seq High-Sensitivity Kit (Illumina).
- Optimize first: Fragment size, DNA recovery, adapter dilution, PCR cycle number, duplicate rate, and positive or negative qPCR QC before sequencing.
1
Confirm ChIP enrichment before library prep
Run ChIP-qPCR on at least one positive and one negative locus before committing samples to sequencing. Proceed when target IP shows clear enrichment over IgG and negative loci.
2
Quantify ChIP DNA carefully
Use a sensitive fluorometric method or library prep kit guidance for low-input DNA. ChIP DNA may be below the accurate range of standard absorbance methods.
3
Assess fragment size
Check purified ChIP DNA or library intermediates by Bioanalyzer, TapeStation, Fragment Analyzer, or gel-based method. Many ChIP-seq workflows use enriched DNA around 150-500 bp before library amplification.
4
Prepare library with low-input conditions
Use a ChIP-seq compatible low-input DNA library kit such as the EpiNext ChIP-Seq High-Sensitivity Kit (Illumina). Follow kit-specific end repair, A-tailing, adapter ligation, cleanup, and PCR conditions. Dilute adapters when DNA input is low to reduce adapter dimers.
5
Optimize PCR cycle number
Use the fewest PCR cycles that produce enough library for sequencing. Excess PCR can increase duplicate reads, skew enrichment, and create library artifacts.
6
Clean up and size select library
Use magnetic bead cleanup or kit-recommended size selection to remove primers, enzymes, salts, and adapter dimers. Verify final library size distribution before pooling.
7
Quantify final library
Quantify libraries using qPCR-based library quantification or another sequencing-compatible method. Normalize samples before pooling.
8
Review sequencing design
Include biological replicates, matching input controls, and IgG controls when informative. For broad histone marks, plan sufficient depth and appropriate peak-calling settings. For narrow transcription factor peaks, prioritize enrichment and replicate consistency.
Library artifactsAdapter dimer and high PCR duplication often indicate too little input DNA, excess adapter, or too many PCR cycles.
ReplicatesBiological replicate consistency is more useful than a single high-depth library with poor ChIP enrichment.
ChIP reference notes
Buffer starting pointsCross-linking ChIP often uses low-salt wash, high-salt wash, LiCl wash, and TE wash buffers. Native ChIP usually needs milder conditions to preserve nucleosome recovery.
Antibody controlsUse input, IgG control, no-antibody or beads-only control, positive locus, negative locus, and a known ChIP-positive antibody when setting up a new assay.
Target typeHistone marks are often more robust in ChIP than low-abundance transcription factors. Transcription factors usually require tighter optimization of crosslinking and antibody conditions.
FragmentationUse sonication or MNase conditions that match the workflow. Confirm fragment size every time sample type, fixation time, cell number, or sonicator settings change.
Wash stringencyIncrease salt or detergent only when background remains high. Excessive stringency can reduce real target recovery, especially for weak or low-abundance targets.
Common problemsNo enrichment often reflects poor chromatin quality, over-crosslinking, poor antibody performance, low target abundance, or non-functional primers. High IgG background often reflects bead blocking, wash stringency, or excessive chromatin input.
This protocol provides starting conditions for research use. Use the product datasheet, sample type, antibody validation data, and laboratory safety requirements to finalize conditions for a specific experiment.
