library_construction_protocol: Fresh testes were collected from wild-type and Nkapl KO mice at postnatal day 21, ground into powder in liquid N2, and crosslinked by 1% formaldehyde, followed by quenching with glycine solution. Chromatin was fragmented by sonication in ChIP SDS lysis buffer (50 mM Tris-HCl, pH=8; 10 mM EDTA, pH=8; 1% SDS) using the Covaris-S220 sonicator. Crosslinked chromatin was incubated with indicated antibodies in ChIP dilution buffer (50 mM HEPES, pH7.5, 155 mM NaCl, 1.1% Triton X-100, 0.11% Na-deoxycholate) with protease inhibitors overnight. Crosslinking was reversed overnight at 65°C, and DNA was extracted by using phenol/chloroform/isoamyl alcohol. Precipitated DNA was amplified for deep-sequencing. For ChIP-seq, equal DNA was amplified according to ChIP Sequencing Sample Preparation Guide provided by Illumina using adaptors and primers.