Freshly isolated thymocytes cross-linked with 1% formaldehyde. Nuclei were isolated from the cells and lysed in Lysis Buffer by sonication. The lysate was incubated with rabbit anti-TCF1 antibody (CST, C46C7) pre-bound to Dynabeads® M-280 Sheep anti-Rabbit IgG overnight at 4 oC. Chromatin DNA was reverse-crosslinked and eluted. Samples were treated with RNase A and Proteinase K, and precipitated chromatin DNA was purified by use of ChIP DNA Clean & ConcentratorTM (ZYMO Research, CA). Purified DNA was subjected to the re-sonication with a Covaris S220 to produce DNA fragments with an average size of 200 bp, and was used for library preparation with NEBNext ChIP-seq Library Prep Master Mix Set for Illumina and NEBNext Multiplex Oligos for Illumina (New England BioLabs). Sequencing was performed by Immugen with NovaSeq X.