Abstract
Actively transcribed regions of the genome are protected by transcription-coupled DNA repair mechanisms, including transcription-coupled homologous recombination (TC-HR). Here we used reactive oxygen species (ROS) to induce and characterize TC-HR at a transcribed locus in human cells. As canonical HR, TC-HR requires RAD51. However, the localization of RAD51 to damage sites during TC-HR does not require BRCA1 and BRCA2, but relies on RAD52 and Cockayne Syndrome Protein B (CSB). During TC-HR, RAD52 is recruited by CSB through an acidic domain. CSB in turn is recruited by R loops, which are strongly induced by ROS in transcribed regions. Notably, CSB displays a strong affinity for DNA:RNA hybrids in vitro, suggesting that it is a sensor of ROS-induced R loops. Thus, TC-HR is triggered by R loops, initiated by CSB, and carried out by the CSB-RAD52-RAD51 axis, establishing a BRCA1/2-independent alternative HR pathway protecting the transcribed genome.
Highlights
Transcribed regions of the genome are protected by transcription-coupled DNA repair mechanisms, including transcription-coupled homologous recombination (TC-HR)
These results suggest that ROSinduced R loops in transcribed regions trigger TC-HR through the Cockayne Syndrome Protein B (CSB)-RAD52-RAD51 axis, revealing the framework of an alternative HR pathway that protects the transcribed genome against reactive oxygen species (ROS)-induced DNA damage
CSB-FL displayed a much higher affinity for DNA:RNA hybrids than RAD52 (Fig. 5d). These results suggest that both CSB and RAD52 may directly recognize the R loops at sites of DNA damage, and that CSB may enhance the recruitment of RAD52 to R loops by binding to both R loops and RAD52
Summary
Transcribed regions of the genome are protected by transcription-coupled DNA repair mechanisms, including transcription-coupled homologous recombination (TC-HR). We showed that ROS activated TC-HR at a transcriptionally active locus, thereby implicating TC-HR in the repair of ROS-induced DNA damage in transcribed regions Despite these tantalizing features, TC-HR is still poorly understood as a pathway. The recruitment of CSB requires DNA:RNA hybrids, which are strongly induced by ROS in the transcribed region. CSB directly and robustly binds to DNA:RNA hybrids, suggesting that it is a sensor of ROS-induced R loops in transcribed regions. Together, these results suggest that ROSinduced R loops in transcribed regions trigger TC-HR through the CSB-RAD52-RAD51 axis, revealing the framework of an alternative HR pathway that protects the transcribed genome against ROS-induced DNA damage
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
