Human genomic DNA is widely interspersed with i-motif structures

DNA i-motif structures are formed in the nuclei of human cells and are believed to provide critical genomic regulation. While the existence of i-motif structures in human cells has been demonstrated by immunofluorescent staining and by the characterisation of select model genes, the abundance and distribution of such structures in the human genome have remained unclear. Here we utilise high affinity i-motif immunoprecipitation followed by sequencing to map i-motifs in the genomic DNA of human MCF7, U2OS and HEK293T cells. Validated by biolayer interferometry and circular dichroism spectroscopy, our approach identified i-motif structures that are widely distributed throughout the human genome and are common in genes upregulated in G0/G1 cell cycle phases.