title: Tuning in to interference: R-loops and cascade complexes in CRISPR immunity.
abstract: Stable RNA-DNA hybrids formed by invasion of an RNA strand into duplex DNA, termed R-loops, are notorious for provoking genome instability especially when they arise during transcription. However, in some instances (DNA replication and class switch recombination), R-loops are useful so long as their existence is carefully managed to avoid them persisting. A recent flow of research papers establishes a newly discovered use for R-loops as key intermediates in a prokaryotic immune system called CRISPR (Clustered Regularly Interspersed Short Palindromic Repeats). Structures and mechanism of ribonucleoprotein complexes ("Cascades") that form CRISPR R-loops highlight precision targeting of duplex DNA that has sequence characteristics marking it as foe, enabling nucleolytic destruction of DNA and recycling the Cascade. We review these significant recent breakthroughs in understanding targeting/interference stages of CRISPR immunity and discuss questions arising, including a possible link between targeting and adaptive immunity in prokaryotes.
authors: Department of Molecular Biology, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia.
authors: Ivana
authors: I
authors: Ivančić-Baće
authors: School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham NG7 2UH, UK.
authors: Jamieson
authors: J
authors: Al Howard
authors: School of Biomedical Sciences, University of Nottingham Medical School, Queens Medical Centre, Nottingham NG7 2UH, UK. Electronic address: ed.bolt@nottingham.ac.uk.
authors: Edward L
authors: EL
authors: Bolt
mesh_terms: D004247:DNA / Q000378:metabolism*; D006868:Hydrolysis; D008954:Models, Biological; D009693:Nucleic Acid Hybridization; D011387:Prokaryotic Cells / Q000502:physiology*; D011995:Recombination, Genetic; D012261:Ribonucleoproteins / Q000378:metabolism*
chemical_list: D012261:Ribonucleoproteins; D004247:DNA