R-loops are abundant three-stranded nucleic-acid structures that form
- NSF-PAR ID:
- 10087742
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 116
- Issue:
- 13
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 6260-6269
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Segal, R. ; Shtylla, B. ; Sindi, S (Ed.)R-loops are nucleic acid structures consisting of a DNA:RNA hybrid and a DNA single strand. They form naturally during transcription when the nascent RNA hybridizes to the template DNA, forcing the coding DNA strand to wrap around the RNA:DNA duplex. Although formation of R-loops can have deleterious effects on genome integrity, there is evidence of their role as potential regulators of gene expression and DNA repair. Here we initiate an abstract model based on formal grammars to describe RNA:DNA interactions and the formation of R-loops. Separately we use a sliding window approach that accounts for properties of the DNA nucleotide sequence, such as C-richness and CG-skew, to identify segments favoring R-loops. We evaluate these properties on two DNA plasmids that are known to form R-loops and compare results with a recent energetics model from the Chédin Lab. Our abstract approach for R-loops is an initial step toward a more sophisticated framework which can take into account the effect of DNA topology on R-loop formation.more » « less
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Abstract G-quadruplex (G4) is a noncanonical secondary structure of DNA or RNA which can enhance or repress gene expression, yet the underlying molecular mechanism remains uncertain. Here we show that when positioned downstream of transcription start site, the orientation of potential G4 forming sequence (PQS), but not the sequence alters transcriptional output. Ensemble in vitro transcription assays indicate that PQS in the non-template increases mRNA production rate and yield. Using sequential single molecule detection stages, we demonstrate that while binding and initiation of T7 RNA polymerase is unchanged, the efficiency of elongation and the final mRNA output is higher when PQS is in the non-template. Strikingly, the enhanced elongation arises from the transcription-induced R-loop formation, which in turn generates G4 structure in the non-template. The G4 stabilized R-loop leads to increased transcription by a mechanism involving successive rounds of R-loop formation.
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