# RNase H1 and Sen1 ensure that transient TERRA R-loops promote the repair of short telomeres

## TL;DR

This study shows that temporary RNA-DNA hybrids at short telomeres help repair DNA and delay aging in yeast.

## Contribution

The study reveals that RNase H1 and Sen1 regulate transient RNA-DNA hybrids to promote telomere repair and prevent early senescence.

## Key findings

- RNase H1 and Sen1 are recruited to short telomeres to remove RNA-DNA hybrids.
- Transient RNA-DNA hybrids are essential for efficient DNA repair and delaying replicative senescence.
- Loss of RNase H2 at short telomeres allows RNA-DNA hybrid accumulation, which is counteracted by RNase H1 and Sen1.

## Abstract

Telomere repeat-containing RNA (TERRA) is transcribed at telomeres and forms RNA–DNA hybrids. In budding yeast, the presence of RNA–DNA hybrids at short telomeres promotes homology-directed repair (HDR) and prevents accelerated replicative senescence. RNA–DNA hybrids at telomeres have also been demonstrated to prevent 5′end resection, an essential step for HDR. In accordance, we now demonstrate that, not only the presence, but also the removal, of RNA–DNA hybrids drives HDR at shortened telomeres during replicative senescence. Although RNase H2 is absent from short telomeres, it is quickly compensated for by the recruitment of RNase H1 and Sen1. The recruitment of RNase H1 is essential to allow for the loading of Rad51, consistent with the notion that RNA–DNA hybrids prevent Exo1-mediated end resection. In the absence of RNase H1 or Sen1 function, yeast cultures prematurely enter replicative senescence in the absence of telomerase. Furthermore, the delayed senescence phenotype observed when RNase H2 is deleted, depends on the presence of RNase H1 and Sen1. This study demonstrates the importance of transient RNA–DNA hybrids at short telomeres to regulate senescence.

RNase H2 dissociates from shortened telomeres allowing the stabilization of RNA–DNA hybrids to drive repair. RNase H1 is subsequently recruited to telomeres to ensure the hybrids are transient; a critical feature to prevent early senescence.

R-loops at telomeres promote repair and prevent premature senescence as telomeres shorten.The RNA–DNA hybrids must be of a transient nature to promote DNA repair.Loss of RNase H2 at short telomeres allows R-loop accumulation.RNase H1 and Sen1 promote subsequent RNA–DNA hybrid removal which allows for efficient Rad51 loading and repair.

R-loops at telomeres promote repair and prevent premature senescence as telomeres shorten.

The RNA–DNA hybrids must be of a transient nature to promote DNA repair.

Loss of RNase H2 at short telomeres allows R-loop accumulation.

RNase H1 and Sen1 promote subsequent RNA–DNA hybrid removal which allows for efficient Rad51 loading and repair.

RNase H2 dissociates from shortened telomeres allowing the stabilization of RNA–DNA hybrids to drive repair. RNase H1 is subsequently recruited to telomeres to ensure the hybrids are transient; a critical feature to prevent early senescence.