An R-loop is a structure that forms when an RNA transcript stays bound to the DNA strand that encodes it and leaves the complementary strand exposed as a loop of single stranded DNA. R-loops accumulate when the processing of RNA transcripts is impaired. The failure to remove these RNA-DNA hybrids can lead to replication fork stalling and genome instability. Resolution of R-loops is thought to be mediated mainly by RNase H enzymes through the removal and degradation of the RNA in the hybrid. However, DNA helicases can also dismantle R-loops by displacing the bound RNA. In particular, the Pif1 family DNA helicases have been shown to regulate R-loop formation at specific genomic loci, such as tRNA genes and centromeres. Here we review the roles of Pif1 family helicases in vivo and in vitro and discuss evidence that Pif1 family helicases act on RNA-DNA hybrids and highlight their potential roles in complementing RNase H for R-loop resolution.

中文翻译：

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Pif1家族DNA解旋酶：RNase H的助手？

R环是当RNA转录本与编码它的DNA链保持结合，而互补链暴露为单链DNA环时形成的结构。当RNA转录物的加工受损时，R环会积累。无法去除这些RNA-DNA杂合体会导致复制叉停滞和基因组不稳定。据认为，R-环的分解主要由RNase H酶通过除去杂合体中的RNA并使其降解来介导。但是，DNA解旋酶也可以通过置换结合的RNA来消除R环。特别是，已显示Pif1家族DNA解旋酶可调节特定基因组位点（例如tRNA基因和着丝粒）的R环形成。