Practice question

In vivo DNA-protein interactions are dynamic and easily disrupted during extraction. Chromatin Immunoprecipitation utilizes formaldehyde crosslinking to generate reversible covalent methylene bridges between lysine residues of proteins and exocyclic amines of DNA bases located within two angstroms. This chemical freezing preserves native regulatory assemblies at defined time point, prevents dissociation during cell lysis, sonication and stringent washes, and maintains chromatin architecture. Reversal by heat releases DNA for analysis. Crosslinking therefore secures transient transcription factor binding and does not denature DNA, remove histones or label probes.