Reader Domain Assays
Target-specific Assays

Bromodomain Assay Service (Reader Domain Assays)

Bromodomain screening and profiling of reader domains such as Tudor and chromodomains are performed at Reaction Biology via Thermo Shift, HTRF and AlphaScreen assays.

More than 85 bromodomain assays and 30 other epigenetic reader domain assays are available for screening, lead optimization, or selectivity profiling for reader domain inhibitors.

Several potent bromodomain inhibitors have recently been identified, increasing the appreciation of the reader domain family’s functional importance and therapeutic potential.

At Reaction Biology, we are continuously developing new reader domain assays.

  • Extensive coverage of the bromodomain family. We feature the largest bromodomain assay panel in the industry.
  • All bromodomain proteins and other reader domain proteins are produced at our facility and are available for purchase.
  • The BromoMELTTM assay kit is available for in-house bromodomain inhibitor screening for selectivity profiling.
  • Reader domain inhibitor screening is performed with AlphaScreen, HTRF or Thermal shift assay formats.

Reaction Biology performs bromodomain assay services at our screening facility in Malvern, Pennsylvania. Our reader domain assay service’s typical turnaround time is 10 business days. Reach out to the business development manager in your area to receive a quotation.

The Largest Bromodomain Assay Panel in Industry

Bromodomain proteins are epigenetic readers that bind to acetylated lysine residues on histones and regulate gene transcription. The phylogenetic tree shows the relationships between genes predicted to encode for bromodomain proteins.

all bromodomain containing epigenetic targets shown as a phylogenetic treee

Assay Details

  • Assay format: AlphaScreen
  • Assay format: Thermal Shift
  • Assay format: HTRF
  • Assay setup
  • Monthly screening schedule
  • Selectivity Profiling
  • Cell-based Bromodomain Testing
Assay format: AlphaScreen

AlphaScreen assays stand for amplified luminescent proximity homogeneous assay.

Example of bromodomain BRD-1: The His-tagged bromodomain and the substrate, which is a biotin-tagged acetylated peptide, are each captured on AlphaScreen beads. Binding interaction between the peptide and the bromodomain brings the beads in close proximity. Laser excitation of the donor beads allows for energy transfer by singlet oxygen atoms between the fluorophores.
Incubation with test molecules binding to the bromodomain results in a diminished interaction with the biotinylated substrate leading to a decline in light emission.

Assay format: Thermal Shift

Thermal shift assays measure the thermal stability of a target protein and the increase in protein melting temperature upon the binding of a ligand to the protein. Our thermal shift bromodomain assays are available as service and as a kit for in-house selectivity screening.



Differential Scanning Fluorimetry of BRD2-Tndm (His) in the Presence or Absence of JQ1. Thermal denaturation of BRD2-Tndm (His) was detected by increased binding and fluorescence of the dye SYPRO Orange. Addition of the BET bromodomain inhibitor JQ1 stabilizes the protein folding and shifts the melting temperature from 41 to 44 degrees Celsius.

Assay format: HTRF

HTRF (Homogeneous Time-Resolved Fluorescence) is an assay technology that combines fluorescence resonance energy transfer technology (FRET) with time-resolved measurement (TR) for measuring molecular interactions in a homogeneous format.

HTRF makes use of rare earth complexes such as Europium or Terbium cryptates. These chelates are very stable under a wide range of chemical conditions, are not subject to photobleaching, and show high kinetic stability. HTRF allows enhanced assay performance compared to conventional fluorescent probes in terms of sensitivity, assay window, and robustness.

HTRF assay procedure with a bromodomain: Acetylated peptides are used as substrates for the bromodomains to bind on. Antibodies recognizing the GST tagged-bromodomain are coupled with the donor fluorophore. The peptide is tagged with biotin and recognized by streptavidin which is coupled with an acceptor fluorophore. The proximity of acceptor and donor fluorophore allows for FRET upon excitation.

Incubation with test molecules binding to the bromodomain results in a diminished interaction with the biotinylated substrate leading to a decline in light emission.

Assay setup

Setups: Single-dose screening in duplicates or IC50 value determination with 5 or 10 concentrations. Other screening formats are available upon request.

The thermal shift assay format allows a ‘yes’ or ‘no’ answer whether the test molecule binds to the reader domain protein. IC50 determination is not possible.

Controls: No inhibitor (DMSO vehicle) control and for every assay, one target-specific control compound is tested in 10-dose IC50 format.

Turnaround time: 10 business days for standard projects. Expedited scheduling and data delivery can be arranged prior to the commencement of the studies.

Report: The raw data, % inhibition and control compound IC50 values will be reported in Excel format for single-dose assays. For IC50 orders, raw data, IC50 values, and curve fitting will be delivered in Excel format. Assay conditions, target, and substrate information are available upon request. Requirements for this information should be noted prior to the commencement of the study.

Screening facility: This assay is performed at our screening facility in Malvern, PA, US.

Compound requirements: In brief, for a standard project, 20 µl of a 10 mM DMSO stock or solid material is needed. Less material is needed for large-scale screening. Please refer to our FAQs for information regarding compound preparation and shipping.

Monthly screening schedule

On a monthly basis, Reaction Biology performs compound screening on the full bromodomain panel.

Please see the upcoming screening dates here.

Selectivity Profiling

For more information about the selectivity screening of bromodomain proteins visit our BromoMELTTM Assay Kit page

Cell-based Bromodomain Testing

We offer two assay formats for intracellular compound screening on bromodomain targets:

1. Binding of a compound to BET Bromodomain in intact cells based on NanoBRET Intracellular Target Engagement assay technology.

2. Testing the protein-protein interaction of bromodomains with acetylated histones in intact cells based on the NanoBRET Bromodomain/Histone Interaction Assay.

Please see more information on our Cell-based Epigenetic Assays webpage.