DNA was isolated from E2A-deficient pre-pro-B and pro-B cells, sonicated, end-repaired using the End-It procedure (Epicentre) and incubated in the presence of Klenow to add an A base to the 3'-end. TruSeq adapters were then ligated to fragmented DNA and purified using Agarose gel electrophoresis. Bisulfite conversion was performed as described by the manufacturer (MethylCode). Bisulfite treated DNA was amplified using a TruSeq PCR primer cocktail and Pfu Turbo Cx Polymerase, agarose purified and sequenced on an Illumina HiSeq 2000 sequencer.