A genome-wide and cotranscriptional suppressor of R loops.

R loops arise from hybridization of RNA transcripts with template DNA during transcription. Unrepaired R loops lead to transcription-replication collisions, causing DNA damage and genomic instability. In this issue of Genes & Development, Pérez-Calero and colleagues (pp. 898-912) identify UAP56 as a cotranscriptional RNA-DNA helicase that unwinds R loops. They found that UAP56 helicase activity is required to remove R loops formed from different sources and prevent R-loop accumulation genome-wide at actively transcribed genes.