R Loops: From Transcription Byproducts to Threats to Genome Stability

RNA:DNA hybrid structures known as R loops were thought to be rare byproducts of transcription. In the last decade, however, accumulating evidence has pointed to a new view in which R loops form more frequently, impacting transcription and threatening genome integrity as a source of chromosome fragility and a potential cause of disease. Not surprisingly, cells have evolved mechanisms to prevent cotranscriptional R loop formation. Here we discuss the factors and cellular processes that control R loop formation and the mechanisms by which R loops may influence gene expression and the integrity of the genome.Research in A.A.'s laboratory is funded by the Spanish Ministry of Science and Innovation, Junta de Andalucía, and the European Union (FEDER).Peer reviewe