CNCC: An analysis tool to determine genome-wide DNA break end structure at single-nucleotide resolution

DNA double-stranded breaks (DSBs) are potentially deleterious events in a cell. The end structures (blunt, 3’- and 5’-overhangs) at sites of double-stranded breaks contribute to the fate of their repair and provide critical information for consequences of the damage. Here, we describe the use of a coverage-normalized cross correlation analysis (CNCC) to process high-precision genome-wide break mapping data, and determine genome-wide break end structure distributions at single-nucleotide resolution. For the first time, on a genome-wide scale, our analysis revealed the increase in the 5’ to 3’ end resection following etoposide treatment, and the global progression of the resection due to the removal of DNA topoisomerase II cleavage complexes. Further, our method distinguished the change in the pattern of DSB end structure with increasing doses of the drug. The ability of this method to determine DNA break end structures without a priori knowledge of break sequences or genomic position should have broad applications in understanding genome instability.