RNA-cDNA hybrids mediate transposition via different mechanisms

Retrotransposons can represent half of eukaryotic genomes. Retrotransposon dysregulation destabilizes genomes and has been linked to various human diseases. Emerging regulators of retromobility include RNA-DNA hybrid-containing structures known as R-loops. Accumulation of these structures at the transposons of yeast 1 (Ty1) elements has been shown to increase Ty1 retromobility through an unknown mechanism. Here, via a targeted genetic screen, we identified the rnh1 Delta rad27 Delta yeast mutant, which lacked both the Ty1 inhibitor Rad27 and the RNA-DNA hybrid suppressor Rnh1. The mutant exhibited elevated levels of Ty1 cDNA-associated RNA-DNA hybrids that promoted Ty1 mobility. Moreover, in this rnh1 Delta rad27 Delta mutant, but not in the double RNase H mutant rnh1 Delta rnh201 Delta, RNA-DNA hybrids preferentially existed as duplex nucleic acid structures and increased Ty1 mobility in a Rad52-dependent manner. The data indicate that in cells lacking RNA-DNA hybrid and Ty1 repressors, elevated levels of RNA-cDNA hybrids, which are associated with duplex nucleic acid structures, boost Ty1 mobility via a Rad52-dependent mechanism. In contrast, in cells lacking RNA-DNA hybrid repressors alone, elevated levels of RNA-cDNA hybrids, which are associated with triplex nucleic acid structures, boost Ty1 mobility via a Rad52-independent process. We propose that duplex and triplex RNA-DNA hybrids promote transposon mobility via Rad52-dependent or -independent mechanisms.