Fig. 7.

Model for siRNA-mediated GGR of UV-induced DNA damage. (Left) In the absence of UV-induced DNA damage, some intergenic genomic regions are transcribed by the RNA POL IV to form precursors that are further processed by RDR2. The produced dsRNAs are diced by DCL4 into 21-nt siRNAs and subsequently loaded into an AGO1 nuclear pool that can form a complex with DDB2. (Right) Upon UV-C exposure, CPDs are formed on DNA (yellow triangle). The 21-nt uviRNAs abundance is increased either by enhanced stabilization of 21-nt uviRNAs or of their dsRNA precursors or by increased DCL4 activity. The DDB2-AGO1-uviRNAs complex is loaded on chromatin at damaged sites. DDB2 would allow recognition of CPDs, and AGO1-uviRNAs would allow stabilization of the complex in an RNA−DNA complementary sequence manner. Upon this recognition step, the DDB2−AGO1−uviRNAs complex is released in an ATR-dependent manner from the damaged sites, allowing the next steps of the GGR to efficiently occur.