Genome-wide mapping of G-quadruplex structures with CUT&Tag

ABSTRACT Single-stranded genomic DNA can fold into G-quadruplex (G4) structures or form DNA:RNA hybrids (R loops). Recent evidence suggests that such non-canonical DNA structures affect gene expression, DNA methylation, replication fork progression and genome stability. When and how G4 structures form and are resolved remains unclear. Here we report the use of Cleavage Under Targets and Tagmentation (CUT&Tag) for mapping native G4 in mammalian cell lines at high resolution and low background. Mild native conditions used for the procedure retain more G4 structures and provide a higher signal-to-noise ratio than ChIP-based methods. We determine the G4 landscape of mouse embryonic stem cells (mESC), observing widespread G4 formation at active promoters, active and poised enhancers. We discover that the presence of G4 motifs and G4 structures distinguishes active and primed enhancers in mESCs. Further, performing R-loop CUT&Tag, we demonstrate the genome-wide co-occurence of single-stranded DNA, G4s and R loops, suggesting an intricate relationship between transcription and non-canonical DNA structures.