Q1: Methodological Application – Mapping 3D Genomic Architecture You are investigating a novel transcription factor (TF) and wish to distinguish its direct DNA binding sites from its indirect 3D contact sites (where it interacts with distant loci via looping). Based on the strategies described in the CUT&RUN research and Hi-C protocols, propose an experimental workflow using two distinct methodologies to map these interactions at near base-pair resolution. Why is traditional X-ChIP-seq insufficient for making this specific distinction?

What are the three steps to distinguish direct TF binding sites from indirect 3D contact sites?

1) Perform native ChIP-seq to map direct binding sites. 2) Perform CUT&RUN to map both direct and indirect sites. 3) Compare results: sites in both = direct; sites only in CUT&RUN = indirect 3D contact sites.

Why is traditional X-ChIP-seq insufficient for distinguishing direct from indirect TF binding sites?

1) Formaldehyde crosslinking preserves both direct and indirect interactions indiscriminately. 2) No systematic way to tell if binding is direct or via 3D looping. 3) Low resolution (~2 kb) compared to CUT&RUN, plus high background noise.

What is the first methodological step to map direct binding sites of a TF?

Perform native ChIP-seq without formaldehyde crosslinking. It maps only direct binding sites because protein-protein interactions are transient and do not survive.

What does native ChIP-seq capture?

Only direct binding sites containing the specific DNA-binding motif for the TF.

What is the second methodological step, and what does it capture?

Perform CUT&RUN (Cleavage Under Targets and Release Using Nuclease). It captures both direct binding sites and indirect 3D contact sites.

Why does CUT&RUN capture indirect 3D contact sites?

Because it is performed in situ within intact nuclei, so it preserves spatial proximity interactions.

How do you distinguish direct binding sites from indirect 3D contact sites by comparing the two methods?

Sites found in both native ChIP and CUT&RUN = direct binding sites. Sites found only in CUT&RUN = indirect 3D contact sites.

How can indirect 3D contact sites identified by CUT&RUN be further validated?

Using Hi-C data to confirm they correspond to known high-frequency genomic interacti