Figure 1.

Schematic views of a transcriptional R-loop and two potential mechanisms to avoid it. (A) Nascent RNA re-anneals with the template DNA strand forming an R-loop. (B) A crowded DNA is difficult in forming R-loops with the nascent RNA molecules. (C) The effects of introns in avoiding R-loops. The green lines represent introns while the black lines represent the exons. The first intron of the nascent RNA has been spliced out while the second intron is being spliced. Removal of introns reduces the complementarity of the RNA molecule with the template DNA, meanwhile tethering exon together during transcription prevent the spatial juxtaposition between a nascent RNA and the template DNA.