The C. elegans N2 strain mixed-stage embryos were cross-linked in 2% formaldehyde for 30 min at 25ºC. Chromatin extract was prepared by sonication in FA buffer (50 mM HEPES/KOH pH 7.5, 1 mM EDTA, 1% Triton X-100, 0.1% sodium deoxycholate; 150 mM NaCl). Five to ten micrograms of antibodies were immobilized on sepharose beads and incubated with the chromatin extract for >12 hours at 4ºC. After washing the immunoprecipitants followed by RNase treatment and reverse-crosslinking, DNA were extracted and purified. DNA was blunt-ended and A-overhanged with Exo(-) Klenow fragment in the presence of dATP. DNA fragments were ligated with adaptors. DNA was amplified by PCR with single-end primers. Amplicon was loaded on an agarose gel, and DNA at 200-500 bp was recovered from the gel.