array technology chromatin immunoprecipitation array PSI-MI chip-chip The method combines a modified chromatin immunoprecipitation (ChIP) procedure, with DNA microarray analysis. Cells are fixed with formaldehyde, harvested, and disrupted by sonication. The DNA fragments cross-linked to a protein of interest are enriched by immunoprecipitation with a specific antibody. After reversal of the cross-links, the enriched DNA is amplified and labeled with a fluorescent dye (Cy5) by using a ligation-mediatedpolymerase chain reaction (LM-PCR). In parallel a sample of DNA that is not enriched by immunoprecipitation is subjected to LM-PCR in the presence of a different fluorophore (Cy3), and both immunoprecipitation (IP)-enriched and unenriched pools of labeled DNA were hybridized to a single DNA microarray containing a set of intergenic sequences. The ratio of the Cy5 to Cy3 fluorescence intensities measured at each DNA element in the microarray provided a measure of the extent of binding of the transcription factor to the corresponding genomic locus. MI:0225 chromatin immunoprecipitation assay