ChIP protocol: OCI-Ly7 cells were fixed with 1% formaldehyde, lysed and sonicated to generate fragments less than 500bp. Sonicated lysates were incubated with antibodies overnight and after increasing stringency washes immunocomplexes were recovered and DNA was isolated. Genomic DNA-fragment libraries were prepared using the Illumina ChIP-seq Library preparation Kit following the manufacture’s instructions (Illumina, CA). Briefly 10ng of purified ChIP DNA was end repaired by conversion of overhangs into phosphorylated blunt ends with the use of T4 DNA polymerase and E. coli DNA polymerase I Klenow fragment. Illumina single-end adapters were ligated to the ends of the DNA fragments. Ligation products were purified on a 2% agarose gel with a size selection of 200-300bp. Fifteen PCR cycles were performed with Illumina genomic DNA primers that anneal to the ends of the adapters. The purified PCR-amplified fragment libraries were quantified with the use of the PicoGreen dsDNA Quantitation Assay with the Qubit Fluorometer (Invitrogen, CA). The size range of libraries was validated on the Agilent Technologies 2100 Bioanalyzer with the High Sensitivity DNA Kit (Agilent, CA).