| Summary: | The error‐free and efficient repair of DNA double‐strand breaks is extremely important for cell survival. Over the past several years, RNA has been increasingly implicated in the DNA damage response, but the mechanism or mechanisms through which it can act remain poorly understood. Various hypotheses have been made in the literature: RNA as a signalling molecule or as a scaffold; RNA long‐range interactions to reorganise or maintain chromatin structure; RNA as a template for repair. In this thesis, the miRNA biogenesis apparatus was demonstrated to be involved in DNA repair outside of their normal roles in miRNA maturation. Drosha was required for efficient repair by the two major repair pathways, suggesting a central role in the DNA damage response. Previous reports looking at the involvement of Drosha in DNA damage had suggested that Drosha processes newly transcribed RNA, the product of which would carry out a role in repair. Here, a comprehensive series of nextgeneration sequencing approaches was unable to validate this. Later experiments instead discovered that pre‐existing RNA molecules could participate in repair. RNA invasion around DNA break sites was observed, and shown to be Drosha‐dependent. These damage‐induced DNA:RNA hybrid structures were important for efficient repair, showing that RNA can be a direct and critical mediator of DNA damage repair.
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