Fixed brains and imaginal discs were dissected from 10 third instar larvae. Sonicated chromatin incubated with anti ChIP was performed with 1:100 dilutions of anti-Pho (custom made) and anti-Ph antibodies (a kind gift from Donna Arndt-Jovin), 1:200 dilutions of anti-H3K27me3 (Millipore, 17-622) antibodies, and anti-Engrailed antibodies. Input ChIP DNA (30 ng) was blunt-ended and phosphorylated. A single 'A' nucleotide was added to the 3' ends of the fragments in preparation for ligation to an adapter that has a single-base 'T' overhang. The ligation products were purified and accurately size-selected by agarose gel electrophoresis. Size-selected DNA was purified and PCR-amplified to enrich for fragments that have adapters on both ends. The final purified product was then quantitated before cluster generation.