--- title: "Mapping Regulatory Elements: Accessibility, Occupancy and Contact" description: "Accessibility assays locate enzyme-reachable DNA, occupancy assays map DNA associated with a chosen protein, and contact assays estimate proximity between regions. Match each measurement to its contro" canonical: https://lightmysky.com/learn/science/mapping-regulatory-elements-accessibility-occupancy-and-contact-mt_W2YKGBADJ- source: https://lightmysky.com/learn/science/mapping-regulatory-elements-accessibility-occupancy-and-contact-mt_W2YKGBADJ-.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Mapping Regulatory Elements: Accessibility, Occupancy and Contact Accessibility assays locate enzyme-reachable DNA, occupancy assays map DNA associated with a chosen protein, and contact assays estimate proximity between regions. Match each measurement to its controls and distinguish mapping evidence from a test of regulatory function. Subject: Science · Area: Genetics & Evolution · Ages 22 to 24 Page: https://lightmysky.com/learn/science/mapping-regulatory-elements-accessibility-occupancy-and-contact-mt_W2YKGBADJ- ## Ready when they can - Choose between an accessibility, an occupancy and a contact assay for a stated claim about an element - Distinguish matched input, non-specific antibody background and antibody specificity checks in ChIP-seq, and choose quality checks suited to accessibility and contact assays - Interpret a binned browser-track excerpt and explain why local enrichment alone does not identify a target gene or demonstrate regulatory function ## Lesson: Three questions, three assays ATAC-seq measures DNA reachable by an enzyme. ChIP-seq enriches DNA associated with a chosen protein, directly or through protein partners. Hi-C joins DNA captured nearby and sequences the pairs to estimate contact frequencies. Contact is not permanent touching in every cell. Enhancers and silencers are DNA regions that can increase or reduce transcription, sometimes from far away. These assays map candidates; they do not by themselves establish regulatory effects. *(drawing: Sequencing connects this workflow to the previous topic. Bulk ChIP-seq does not require a separate barcode for every cell.)* For ChIP-seq, matched input samples DNA before antibody enrichment and helps account for fragmentation and mapping biases. A non-specific antibody control checks pull-down background. Neither proves target-antibody specificity; validate that separately and check biological replicates. Comparable signals barely separated from background provide weak evidence of enrichment, not proof of binding or gene activity. Quality checks depend on the assay. For ATAC-seq, check biological replicates, fragment-length patterns and enrichment near transcription start sites, where RNA production begins. For Hi-C, check replicates and account for genomic distance and mapping biases. Nearby regions often contact more frequently. Neither assay is validated by using an antibody background control in place of these checks. Accessibility, protein occupancy and enhancer-associated histone modifications can nominate an element. Contact can suggest a target promoter, where transcription starts. Even together, these observations do not prove regulation. Change or inhibit the element and measure target-gene RNA against matched controls. An effect supports a role in the tested cells, though indirect effects need checking. Results in one cell type do not establish activity in every type. **Example.** This toy table samples two browser tracks in equal-width genomic bins. Values are depth-normalized signal units on a common scale. Interval (bp) ATAC ChIP 100-199 3 2 200-299 24 18 300-399 4 3 Both tracks are highest at 200-299 bp. This locates signal, not a target gene or a regulatory effect. Assay controls are still needed. A genome browser aligns tracks to reference-genome coordinates. ATAC-seq and ChIP-seq peaks show local fragment enrichment; their processing and display scales affect comparison. Hi-C measures pairs of regions, often displayed as a contact map or arcs. A single peak cannot show that pairwise relation. Name the assay's measurement before making a biological claim. **Recap.** Accessibility, occupancy and contact measure different relations. Use assay-specific controls. Mapping nominates candidates; controlled changes test regulatory effects. *Lesson, questions, diagrams and flashcards written for this dataset. Numerical examples are illustrative.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Chromatin: Nucleosomes and Higher-Order Packing](https://lightmysky.com/learn/science/chromatin-nucleosomes-and-higher-order-packing-mt_5q3Hsdqm9x) - [Single-Cell RNA Sequencing: From Droplets to a Count Matrix](https://lightmysky.com/learn/science/single-cell-rna-sequencing-from-droplets-to-a-count-matrix-mt_QCoqY7w_De) ## Opens up - [Genome Engineering: Cut Site, Repair Choice and Editing Outcome](https://lightmysky.com/learn/science/genome-engineering-cut-site-repair-choice-and-editing-outcome-mt_3DqvkO4wdE)