Protocol to capture transcription factor-mediated 3D chromatin interactions using affinity tag-based BL-HiChIP

Pioneer transcription factors (TFs) can directly establish higher-order chromatin interactions to instruct gene transcription. Here, we present a protocol for capturing TF-mediated 3D chromatin interactions using affinity tag-based bridge linker (BL)-Hi-chromatin immunoprecipitation (HiChIP). We describe steps for constructing FLAG-tagged TF, performing BL-HiChIP, and preparing the library. We then detail procedures for sequencing, data analysis, and quality control. This protocol has potential applications in 3D chromatin analysis centered on any specific TF in any type of cells without the need of optimal antibodies. For complete details on the use and execution of this protocol, please refer to Ren et al. (2022).¹.