RNase H1 and H2 are differentially regulated to eliminate RNA-DNA hybrids

Abstract

RNA-DNA hybrids are tightly regulated to ensure genome integrity. The RNase H enzymes, RNase H1 and H2, contribute to chromosomal stability through the removal of RNA-DNA hybrids. Loss of RNase H2 function is implicated in human diseases of the nervous system and cancer. To better understand RNA-DNA hybrid dynamics, we have focused on elucidating the regulation of the RNase H enzymes themselves. Using yeast as a model system, we demonstrate that RNase H1 and H2 are controlled in different manners. RNase H2 is regulated in a strict cell cycle dependent manner, both in terms of its R-loop removal, and ribonucleotide excision repair functions. RNase H1, however, can function independent of cell cycle stage to remove R-loops, but appears to become activated in response to high R-loop loads. These results provide us with a more complete understanding of how and when RNA-DNA hybrids are acted upon by the RNase H enzymes. KEYWORDSRNA-DNA hybrid, R-loop, Ribonucleotide excision repair, RNase H1, RNase H2, cell cycle

RNA-cDNA hybrids mediate transposition via different mechanisms

“…1 and 2b). This likely reflects a higher reliance of cells on Rnh1 over Rnh201 27,28 . Together, the rnh1Δ rad27Δ and rnh1∆ rnh201∆ mutants provide an ideal context for identifying the mechanism by which RNA-DNA hybrids may induce Ty1 retromobility.…”

Molecular and physiological consequences of faulty eukaryotic ribonucleotide excision repair

“…Another simple interpretation of these results would be that RNase H2 interacts with additional replisome components other than PCNA, which too may assist RNase H2 delivery to rNMPs. All other, non-catalytic RNase H2 subunit proteins are constitutively expressed throughout the cell cycle, and the complex resides exclusively within the nuclear compartment (Reijns et al, 2012;Lockhart et al, 2019). In any case, the significance of the PIP-box within the RNase H2 complex requires clarification.…”

“…While RNH201 mRNA expression peaks twice during the yeast cell cycle, during S phase and again during G2/M phase (Arudchandran et al, 2000), the protein accumulates progressively from G1 (where expression is very low) through to M phase (Lockhart et al, 2019). Consistently, upon fractionation of cell lysates, RNase H2 is more prominently chromatin-associated in G2/M than in S phase, but to a lesser extent in G1 (Lockhart et al, 2019), suggesting that postreplicative chromatin association of RNase H2 may be a more general feature and not just restricted to telomeres. Thus, RER could theoretically be initiated at any given time in the cell cycle.…”

“…All other, non-catalytic RNase H2 subunit proteins are constitutively expressed throughout the cell cycle, and the complex resides exclusively within the nuclear compartment (Reijns et al, 2012;Lockhart et al, 2019). The same work further demonstrated that G2 phase-restricted RNase H2 expression is sufficient to allow its functions both in R-loop removal and RER; while restricting expression to S phase in fact causes defects in Rloop processing as well as RER-related toxicity (Lockhart et al, 2019). However, it is conceivable that RER may somehow be temporally regulated, or even coordinated with other DNA repair activities, in order to avoid untimely DNA nick generation and repair synthesis.…”