Evidence of synergism among three genetic variants in a patient with LMNA-related lipodystrophy and amyotrophic lateral sclerosis leading to a remarkable nuclear phenotype

Binding of the nuclear ribonucleoprotein family member FUS to RNA prevents R-loop RNA:DNA hybrid structures

The protein FUS (FUSed in sarcoma) is a metazoan RNA-binding protein that influences RNA production by all three nuclear polymerases. FUS also binds nascent transcripts, RNA processing factors, RNA polymerases, and transcription machinery. Here, we explored the role of FUS binding interactions for activity during transcription. In vitro run-off transcription assays revealed FUS-enhanced RNA produced by a non-eukaryote polymerase. The activity also reduced the formation of R-loops between RNA products and their DNA template. Analysis by domain mutation and deletion indicated RNA-binding was required for activity. We interpret that FUS binds and sequesters nascent transcripts to prevent R-loops from forming with nearby DNA. DRIP-seq analysis showed that a knockdown of FUS increased R-loop enrichment near expressed genes. Prevention of R-loops by FUS binding to nascent transcripts has the potential to affect transcription by any RNA polymerase, highlighting the broad impact FUS can have on RNA metabolism in cells and disease.

R-Loop Immunoprecipitation: A Method to Detect R-Loop Interacting Factors

R-loops are non-B-DNA structures consisting of an RNA/DNA hybrid and a displaced single-stranded DNA. They arise during transcription and play important biological roles. However, perturbation of R-loop levels represents a source of DNA damage and genome instability resulting in human diseases, including cancer and neurodegeneration. In this chapter, we describe a protocol which allows detection of R-loop interactors using affinity purification with S9.6 antibody, specific for RNA/DNA hybrids, followed by Western blotting or mass spectrometry. Multiple specificity controls including addition of synthetic competitors and RNase H treatment are described to verify the specificity of identified R-loop-binding factors. The identification of new R-loop interacting factors and the characterization of their involvement in R-loop biology provides a powerful resource to study the role of these important structures in health and disease.