Chromatin accessibility was assayed using an adaptation of the assay for transposase accessible-chromatin (ATAC)-seq (Buenrostro et al. 2013) as previously described (King and Klose 2017), using 5x10^5 nuclei. ATAC-seq libraries were prepared by PCR amplification using custom-made Illumina barcodes (Buenrostro et al. 2013) and the NEBNext High-Fidelity 2X PCR Master Mix (NEB). Libraries were purified with two rounds of Agencourt AMPure XP bead cleanup (Agencourt, 1.5X bead:sample ratio), and were sequenced using the Illumina HiSeq 2000 platform using 50 bp single-end reads.