CUT&Tag Protocol: Low-Input Chromatin Profiling and Tagmentation

CUT&Tag (Cleavage Under Targets and Tagmentation) is an antibody-guided epigenomic profiling method that uses a Protein A/G–Tn5 transposase fusion to insert sequencing adapters directly into DNA adjacent to a chromatin-bound target. The method combines target recognition and library generation in situ, enabling high-resolution profiling of histone modifications, transcription factors and other chromatin proteins from low cell inputs.

Kaya-Okur and colleagues introduced CUT&Tag as an efficient method for small samples and single cells. Subsequent streamlined protocols reduced background from accessible DNA and made sequencing-ready libraries possible in a single tube.

Important: antibody specificity, cell/nuclear permeability, secondary-antibody compatibility, pA/G–Tn5 loading and tagmentation conditions all affect signal. Do not transfer conditions blindly between histone marks, transcription factors and sample types.

Protocol at a glance

When to use CUT&Tag

• Profile histone modifications in low-input samples.
• Map selected transcription factors or RNA polymerase occupancy.
• Generate chromatin libraries without conventional sonication.
• Profile small cell populations or selected single-cell implementations.
• Compare epigenomic changes across treatment or differentiation conditions.

Equipment required

• Magnetic rack.
• Refrigerated centrifuge.
• Low-binding PCR tubes.
• Tube rotator or controlled mixing platform.
• Thermocycler.
• DNA purification/size-selection system.
• Fragment analyser for library QC.

Core reagents

• Intact cells or isolated nuclei.
• Concanavalin A magnetic beads.
• Mild permeabilisation buffer.
• Target-specific primary antibody.
• Species-compatible secondary antibody where used.
• Pre-loaded pA/G–Tn5 transposome carrying sequencing adapters.
• Magnesium activation buffer.
• PCR master mix and indexed primers.
• DNA cleanup beads or columns.

Antibody selection

CUT&Tag requires an antibody that recognises the chromatin target in permeabilised intact nuclei. Histone-mark antibodies are often robust positive controls because they bind abundant chromatin features. Transcription-factor targets can require more optimisation because occupancy is lower and epitopes can be sensitive to sample preparation.

• Use a validated positive-control antibody when establishing the method.
• Include an IgG or no-primary control.
• If the primary antibody binds Protein A/G weakly, use a compatible secondary antibody to improve recruitment.
• Record antibody lot and avoid changing lots mid-study without bridging data.

Detailed CUT&Tag protocol

1. Prepare cells or nuclei. Harvest gently and keep nuclei intact. Remove debris that could interfere with bead capture.
2. Bind to ConA beads. Equilibrate magnetic beads and incubate with cells/nuclei using gentle mixing.
3. Permeabilise. Use a mild detergent concentration that permits antibody access without widespread nuclear disruption.
4. Add primary antibody. Incubate under validated conditions, typically cold or at controlled room temperature depending on target and workflow.
5. Wash. Remove unbound primary antibody while preserving bead-bound nuclei.
6. Add secondary antibody if used. Select a species-specific secondary compatible with pA/G recruitment and incubate under controlled conditions.
7. Wash again. Remove free secondary antibody.
8. Add pA/G–Tn5 transposome. Incubate the pre-loaded transposase fusion so it binds antibody-targeted chromatin.
9. Perform stringent wash steps. Free Tn5 can tagment accessible chromatin away from the target and elevate background.
10. Activate tagmentation with Mg²⁺. Incubate for the empirically determined time and temperature. Keep activation identical across comparative samples.
11. Stop the reaction. Use the validated stop chemistry to terminate transposase activity.
12. Recover DNA. Purify tagmented DNA using a method that retains the intended fragment range.
13. Amplify libraries. Use indexed primers and the minimum PCR cycles required for sufficient library recovery.
14. Clean up/size-select. Remove primers and undesired fragments.
15. QC libraries. Measure concentration and fragment-size distribution.
16. Sequence paired-end. Analyse target enrichment relative to matched controls and biological replicates.

Controls and normalisation

• IgG/no-primary control: measures transposase accessibility and non-specific antibody background.
• Positive histone-mark control: confirms that the workflow, pA/G–Tn5 and library preparation are functioning.
• Biological negative control: target knockout/depletion or a condition without occupancy is stronger than IgG alone for specificity.
• Optional spike-in: can support cross-sample normalisation, but should be designed prospectively and analysed consistently.

Optimising tagmentation

Excessive tagmentation can increase accessible-DNA background and compress differences between target and control. Insufficient tagmentation reduces library yield. Optimise pA/G–Tn5 concentration, wash stringency, Mg²⁺ activation time and temperature using a robust positive target before profiling a low-abundance factor.

Library QC and expected fragment patterns

• Low total DNA yield is not automatically a failure; CUT&Tag is designed for low background.
• Histone-mark libraries often show nucleosomal periodicity.
• Transcription-factor libraries can contain shorter fragments around binding sites.
• Over-amplification can distort fragment distribution and increase duplicate reads.
• Compare target enrichment with negative control before committing to deeper sequencing.

CUT&Tag versus CUT&RUN

Warnings and common analytical traps

• Do not assume high library yield means high target specificity.
• Do not let free Tn5 dominate the assay. Wash quality is critical.
• Do not over-amplify low-input libraries.
• Do not use IgG as the only specificity evidence for a new transcription-factor antibody.
• Do not compare libraries prepared with materially different PCR-cycle counts without considering amplification bias.

Limitations

• Requires an antibody that works in permeabilised native chromatin.
• Tn5 has intrinsic accessibility preferences that can contribute background.
• Very low-input libraries are sensitive to PCR bias and sample loss.
• Single-cell variants require additional indexing and analysis infrastructure.

Troubleshooting

Frequently asked questions

How many cells are needed?

CUT&Tag was developed for low-input and single-cell-compatible profiling, but practical requirements depend on target abundance, antibody performance and sequencing depth.

Can a ChIP antibody be used?

It is a candidate, not a guarantee. Validate directly in CUT&Tag because the epitope is presented in native permeabilised chromatin.

Why use a secondary antibody?

It can improve recruitment of Protein A/G–Tn5 to primary antibodies with weaker Protein A/G binding and can amplify tethering density.

References and journal sources

1. Kaya-Okur HS et al. CUT&Tag for efficient epigenomic profiling of small samples and single cells. Nat Commun. 2019;10:1930. doi:10.1038/s41467-019-09982-5.
2. Kaya-Okur HS et al. Efficient low-cost chromatin profiling with CUT&Tag. 2020. PMID:32913232.
3. Simplified Epigenome Profiling Using Antibody-tethered Tagmentation. Bio Protoc. 2021;11:e4043.

Relevant ABMIUM products

• Anti-Human/Mouse/Rat Histone H3 Antibody [B552] — the ABMIUM catalogue explicitly lists this antibody for ChIP and CUT&Tag among its applications. Confirm the target/species and supporting documents before use.

Explore more with ABMIUM

For another histone mark or transcription factor, use Find your MATCH to compare application evidence. Related workflows: ChIP and CUT&RUN.