Harmful DNA:RNA hybrids are formedin cisand in a Rad51-independent manner

DNA:RNA hybrids constitute a well-known source of recombinogenic DNA damage. The current literature is in agreement with DNA:RNA hybrids being produced co-transcriptionally by the invasion of the nascent RNA molecule producedin ciswith its DNA template. However, it has also been suggested that recombinogenic DNA:RNA hybrids could be facilitated by the invasion of RNA molecules producedin transin a Rad51-mediated reaction. Here, we tested the possibility that such DNA:RNA hybrids producedin transconstitute a source of recombinogenic DNA damage taking advantage of Rad51-independent single-strand annealing recombination assays and new constructs designed to induce expression of mRNA transcriptsin transin the yeastSaccharomyces cerevisiae.We show that unscheduled and recombinogenic DNA:RNA hybrids are formed incisduring transcription and in a Rad51-independent manner.