Elongation Factor TFIIS Prevents Transcription Stress and R-Loop Accumulation to Maintain Genome Stability [ RNA-seq]

Connections between RNA polymerase II (RNAPII) transcription stress, R-loops, and genome instability have been established however, the underlying mechanisms remain poorly understood. Here we used a mutant version of elongation factor TFIIS (TFIISmut) to specifically induce increased levels of RNAPII pausing, arrest, and/or backtracking in human cells. TFIISmut expression results in slower elongation rates, relative depletion of polymerases from the end of genes, and increased levels of stopped RNAPII. It affects mRNA splicing and termination as well. Remarkably, however, TFIISmut expression also dramatically increases R-loops, which may form at the anterior end of backtracked RNAPII and trigger genome instability, including DNA strand breaks. These results shed new light on the relationship between transcription stress and R-loops, and suggest that different classes of R-loops exist, potentially with distinct consequences for genome instability. Overall design: To study RNAPII backtracking and its effects in human cells, we used HEK293 TREX cells in which we overexpressed, under the control of a dox-promoter, a dominant negative form of TFIIS (TFIIS mut), an elongation factor necessary for stimulating RNAPII intrinsic cleavage activity. TFIISmut cells were maintained in the presence of Dox to ensure over-expression for 48 hours prior to harvest..

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Zatreanu D, Han Z, Mitter R, Tumini E, Williams H, Gregersen L, Dirac-Svejstrup AB, Roma S, Stewart A, Aguilera A, Svejstrup JQ