Arginine methylation of the DDX 5 helicase RGG / RG motif by PRMT 5 regulates resolution of RNA:DNA hybrids

Aberrant transcription‐associated RNA : DNA hybrid (R‐loop) formation often causes catastrophic conflicts during replication, resulting in DNA double‐strand breaks and genomic instability. Preventing such conflicts requires hybrid dissolution by helicases and/or RN ase H. Little is known about how such helicases are regulated. Herein, we identify DDX 5, an RGG / RG motif‐containing DEAD ‐box family RNA helicase, as crucial player in R‐loop resolution. In vitro , recombinant DDX 5 resolves R‐loops in an ATP ‐dependent manner, leading to R‐loop degradation by the XRN 2 exoribonuclease. DDX 5‐deficient cells accumulate R‐loops at loci with propensity to form such structures based on RNA : DNA immunoprecipitation ( DRIP )‐ qPCR , causing spontaneous DNA double‐strand breaks and hypersensitivity to replication stress. DDX 5 associates with XRN 2 and resolves R‐loops at transcriptional termination regions downstream of poly(A) sites, to facilitate RNA polymerase II release associated with transcriptional termination. Protein arginine methyltransferase 5 ( PRMT 5) binds and methylates DDX 5 at its RGG / RG motif. This motif is required for DDX 5 interaction with XRN 2 and repression of cellular R‐loops, but not essential for DDX 5 helicase enzymatic activity. PRMT 5‐deficient cells accumulate R‐loops, resulting in increased formation of γH2 AX foci. Our findings exemplify a mechanism by which an RNA helicase is modulated by arginine methylation to resolve R‐loops, and its potential role in regulating transcription.