Interactions of proteins with DNA mediate many critical nuclear functions. Chromatin immunoprecipitation (ChIP) is a robust technique for studying protein-DNA interactions. Current ChIP assays, however, either require large cell numbers, which prevent their application to rare cell samples or small-tissue biopsies, or involve lengthy procedures. We describe here a 1-day micro ChIP (microChIP) protocol suitable for up to eight parallel histone and/or transcription factor immunoprecipitations from a single batch of 1,000 cells. MicroChIP technique is also suitable for monitoring the association of one protein with multiple genomic sites in 100 cells. Alterations in cross-linking and chromatin preparation steps also make microChIP applicable to approximately 1-mm(3) fresh- or frozen-tissue biopsies. From cell fixation to PCR-ready DNA, the procedure takes approximately 8 h for 16 ChIPs.
