Low ChIP Signal Due to Chromatin Over-Fragmentation (ChIP (Low Signal))

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Accepted Answer

Low or absent signal in ChIP experiment despite proper antibody and starting material. Chromatin fragments are smaller than 500 bp after sonication or enzymatic digestion. Common causes: 1) Excessive sonication reducing chromatin fragment size below 500 bp 2) Over-digestion by nuclease displacing nucleosomes from DNA 3) Intranucleosomal DNA becomes digested when fragments are too small 4) Loss of protein-DNA complexes due to disrupted nucleosome structure Solutions: 1) Do not sonicate chromatin to fragment size less than 500 bp 2) For N-ChIP, use enzymatic digestion only (generally sufficient fragmentation) 3) Optimize sonication parameters (amplitude, duration, cycles) to maintain 500-1000 bp range 4) Verify fragment size by agarose gel electrophoresis before proceeding with IP