Quality control of ATAC library: While we require the Agilent Bioanalyzer trace at step 5.3 to contain the five expected peaks (0-nucleosome, 1-nucleosome, 2-nucleosomes, 3-nucleosomes, and multiple-nucleosomes), we are somewhat lenient in the expectation that the 1-nucleosome peak will be higher than the other peaks. If peaks are missing, we don’t proceed with the sample. If the peaks are visible but the material concentration is low, we recommend rebuilding the library from the cDNA step 4.3.