Titration of chromatin relative to a fixed amount of antibody. (a) ChIP titration experiment using an antibody against acetylated H4. Dilution of the chromatin has no effect on the precipitation efficiency. (b) ChIP titration experiment using an antibody against an invariant domain of H3 (H3core). Dilution of the chromatin improves the precipitation efficiency, suggesting that the antibody recognizing the H3core is sensitive to inhibitory factors present in the chromatin sample. ChIP-QPCR was performed as described in this paper. Chromatin was isolated from leaves of 2 week-old plants, sonicated and used in 1:1, 1:2 and 1:4 dilutions for ChIP. The input samples are diluted by the same factors as the chromatin samples. Results are represented as %IP, the error bars indicate the standard error. ChIP samples are represented by closed bars, while open bars indicate the signals from the 'no-antibody' serum controls. Each data point represents the average of two different chromatin samples, each analyzed in duplo.