Mechanism Of Homologous Recombination Mediated By Small RNAs

DNA double-strand breaks (DSBs) are highly cytotoxic lesions and pose a major threat to genome stability if not properly repaired. There are two main types repair pathways for double-stranded breaks: Homologous recombination repair (HR) and Non-homologous end joining repair (NHEJ). NHEJ is an effective and error-prone repair. HR has a strong fidelity, but it needs homologous sequences.We and others have previously shown that there are small RNAs (diRNAs) can be produced in the DSB sites. DiRNAs are associated with Argonaute (Ago) proteins and appear important for DSB repair and DNA damage signaling, though the mechanism remains unclear. Here we report that the role of diRNAs/Ago2complex are very important in homologous recombination (HR) in DSB repair. We show that Ago2forms a complex with Rad51and that the interaction is enhanced in cells treated with ionizing radiation. We demonstrate that Rad51accumulation at DSB sites and HR repair depend on catalytic activity as well as small RNA binding capability of Ago2. In contrast resection of DSB as well as RPAand Mrell loading is unaffected by Ago2or Dicer depletion, suggesting that Ago2functions directly to mediate Rad51accumulation. Taken together, our findings suggest that guided by diRNAs, Ago2can promote Rad51to recruit onto RPA-coated ssDNAs and to facilitate repair by HR. And we also suggests that Drosha and Dicer are not required for DNA damage response signaling. Our findings greatly expand the knowledge of sRNA field provide new mechanisms of DSB repair.