How RNA transcripts coordinate DNA recombination and repair

Abstract

Genetic studies in yeast indicate that RNA transcripts facilitate homology-directed DNA repair in a manner that is dependent on RAD52. The molecular basis for so-called RNA-DNA repair, however, remains unknown. Using reconstitution assays, we demonstrate that RAD52 directly cooperates with RNA as a sequence-directed ribonucleoprotein complex to promote two related modes of RNA-DNA repair. In a RNA-bridging mechanism, RAD52 assembles recombinant RNA-DNA hybrids that coordinate synapsis and ligation of homologous DNA breaks. In an RNA-templated mechanism, RAD52-mediated RNA-DNA hybrids enable reverse transcription-dependent RNA-to-DNA sequence transfer at DNA breaks that licenses subsequent DNA recombination. Notably, we show that both mechanisms of RNA-DNA repair are promoted by transcription of a homologous DNA template in trans. In summary, these data elucidate how RNA transcripts cooperate with RAD52 to coordinate homology-directed DNA recombination and repair in the absence of a DNA donor, and demonstrate a direct role for transcription in RNA-DNA repair.

Fig. 1

Models of RAD52-mediated RNA−DNA repair. a RNA-bridging DSB repair model. RAD52 utilizes RNA to tether both ends of a homologous DSB which forms a DNA synapse for ligation. RNA degradation by RNase H may also occur. b RNA-templated DSB repair model. RAD52 forms an RNA−DNA hybrid along the 3′ overhang of a DSB. The RNA is then used as a template for DNA repair synthesis by RT. The RNA is then degraded by RNase H and RAD52 promotes SSA of the opposing homologous ssDNA overhangs. Final processing of the DSB involves gap filling and ligation

Fig. 2

RAD52 promotes RNA-dependent DNA recombination. a Schematic of assay (left). Non-denaturing gels showing RAD52 RNA−DNA recombination (RNA-bridging of homologous DNA) in the presence of the indicated substrates (right). b Schematic of assay (left). Non-denaturing gel showing RNase H digestion of a RAD52-mediated RNA−DNA recombination intermediate (RNA−DNA recombinant bridge) (right). c Graph showing a time course of RNA–DNA recombination (bridging) compared to DNA−DNA recombination (bridging) of left and right flanking ssDNA without RPA and in the presence and absence of RAD52. Data shown as average ± SD, n = 3. d Schematic of assay (left). Non-denaturing gel showing RAD52 RNA−DNA recombination in the presence of the indicated RPA-coated substrates (right). e Graph showing a time course of RNA−DNA recombination (bridging) compared to DNA−DNA recombination (bridging) of left and right flanking RPA-bound ssDNA in the presence and absence of RAD52. Data shown as average ± SD, n = 3. f Schematic of assay (left). Non-denaturing gel showing RAD51 RNA−DNA recombination (bridging) in the presence of RPA pre-coated substrates (right). g Schematic of assay (left). Non-denaturing gel showing RAD52 RNA−DNA recombination (bridging) of the indicated pssDNA substrates (right). h Schematic of assay (left). Non-denaturing gel showing RAD52 RNA−DNA recombination (bridging) of the indicated RPA-coated pssDNA substrates (right). ^* = ³²P label. % bridging indicated

Fig. 3

RAD52 promotes RNA transcript-dependent DNA recombinational repair. a Schematic of assay (left). Denaturing gel showing RAD52-dependent RNA−DNA repair in the presence of left and right ssDNA flanks and the indicated proteins (right). b Schematic of assay (left). Denaturing gel showing RAD52-dependent RNA−DNA repair in the presence of RPA-coated left and right ssDNA flanks and indicated proteins (right). c Schematic of assay (left). Denaturing gel showing RAD52-mediated RNA transcript-dependent DNA repair in the presence of RPA-coated left and right ssDNA flanks and indicated proteins (middle). Graph showing percent of RNA transcript-dependent DNA recombinational repair (right). Data shown as average ± SD, n = 3. *, p = 0.016 (unpaired Student’s t-test). Sequencing chromatogram of RNA transcript-dependent DNA recombinational repair product (bottom). ^* = ³²P label

Fig. 4

RAD52 promotes RNA-dependent recombinational repair of DSBs. a Schematic of assay (left). Non-denaturing gel showing a time course of RAD52-dependent RNA−DNA recombination (bridging) of blunt-ended DNA in the presence of RPA (middle). Plot showing time course of RAD52-dependent RNA−DNA recombination (bridging) of blunt-ended DNA in the presence of RPA (right). Data shown as average ± SEM, n = 3. b Schematic of assay (left). Non-denaturing gels showing RAD52-dependent RNA−DNA recombination (bridging) of blunt-ended DNA in the presence (left) and absence (right) of RPA. c Schematic of assays showing RAD52-dependent RNA−DNA recombination (bridging) of blunt-ended DNA employing either RAD52-dsDNA pre-incubation (right schematic) or RAD52-RNA (left schematic) pre-incubation steps, and performed either with and without RPA. Graph showing quantification of RAD52-dependent RNA−DNA recombination (bridging) of blunt-ended DNA utilizing the indicated pre-incubation steps and with and without RPA (right). Data shown as average ± SD, n = 3. d Schematic of assay (left). Denaturing gel showing RAD52-dependent RNA−DNA recombinational repair (bridging followed by ligation) of blunt-ended DNA in the presence of the indicated proteins and substrates (middle). Graph showing percent of RAD52-dependent RNA-mediated recombinational repair of blunt-ended DNA (% ligation) (right). Data shown as average ± SD, n = 3. ***, p = 0.0008 (unpaired Student’s t-test). ^* = ³²P label

Fig. 5

RAD52 promotes RNA transcript-templated DNA recombination. a Schematic of assay (left). Denaturing gel showing reverse transcription of a RNA−DNA recombinant half-bridge in the presence of the indicated proteins and RNA (middle). Graph showing percent extension of a RNA−DNA recombinant half-bridge by RT in the presence and absence of RAD52 (right). Data shown as average ± SD, n = 4, ***, p < 0.001 (unpaired Student’s t-test). b Schematic of assay (left). Non-denaturing gel showing RNA-templated DNA recombination in the presence of indicated proteins and RNA and DNA substrates (middle). Graph showing percent of RNA−DNA recombination product in the presence and absence of RAD52 (right). Data shown as average ± SD, n = 4, ***, p < 0.001 (unpaired Student’s t-test). c Schematic of assay (left). Non-denaturing gel showing RAD52-dependent RNA transcript-templated DNA recombination in the presence of the indicated proteins and DNA substrates (middle). Graph showing percent of RNA transcript-templated DNA recombination product in the presence and absence of RAD52 (right). Data shown as average ±SD, n = 3, ***, p < 0.001, (unpaired Student’s t-test). ^* = ³²P label