RNA-templated DNA repair

RNA can act as a template for DNA synthesis in the reverse transcription of retroviruses and retrotransposons(1) and in the elongation of telomeres(2). Despite its abundance in the nucleus, there has been no evidence for a direct role of RNA as a template in the repair of any chromosomal DNA lesions, including DNA double-strand breaks (DSBs), which are repaired in most organisms by homologous recombination or by non-homologous end joining(3). An indirect role for RNA in DNA repair, following reverse transcription and formation of a complementary DNA, has been observed in the non-homologous joining of DSB ends(4,5). In the yeast Saccharomyces cerevisiae, in which homologous recombination is efficient(3), RNA was shown to mediate recombination, but only indirectly through a cDNA intermediate(6,7) generated by the reverse transcriptase function of Ty retrotransposons in Ty particles in the cytoplasm(8). Although pairing between duplex DNA and single-strand (ss) RNA can occur in vitro(9,10) and in vivo(11), direct homologous exchange of genetic information between RNA and DNA molecules has not been observed. We show here that RNA can serve as a template for DNA synthesis during repair of a chromosomal DSB in yeast. The repair was accomplished with RNA oligonucleotides complementary to the broken ends. This and the observation that even yeast replicative DNA polymerases such as alpha and delta can copy short RNA template tracts in vitro demonstrate that RNA can transfer genetic information in vivo through direct homologous interaction with chromosomal DNA.