title: Structures of the RNA-guided surveillance complex from a bacterial immune system.
abstract: Bacteria and archaea acquire resistance to viruses and plasmids by integrating short fragments of foreign DNA into clustered regularly interspaced short palindromic repeats (CRISPRs). These repetitive loci maintain a genetic record of all prior encounters with foreign transgressors. CRISPRs are transcribed and the long primary transcript is processed into a library of short CRISPR-derived RNAs (crRNAs) that contain a unique sequence complementary to a foreign nucleic-acid challenger. In Escherichia coli, crRNAs are incorporated into a multisubunit surveillance complex called Cascade (CRISPR-associated complex for antiviral defence), which is required for protection against bacteriophages. Here we use cryo-electron microscopy to determine the subnanometre structures of Cascade before and after binding to a target sequence. These structures reveal a sea-horse-shaped architecture in which the crRNA is displayed along a helical arrangement of protein subunits that protect the crRNA from degradation while maintaining its availability for base pairing. Cascade engages invading nucleic acids through high-affinity base-pairing interactions near the 5' end of the crRNA. Base pairing extends along the crRNA, resulting in a series of short helical segments that trigger a concerted conformational change. This conformational rearrangement may serve as a signal that recruits a trans-acting nuclease (Cas3) for destruction of invading nucleic-acid sequences.
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA.|Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: Blake
authors.initials: B
authors.lastname: Wiedenheft
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Gabriel C
authors.initials: GC
authors.lastname: Lander
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA.|Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: Kaihong
authors.initials: K
authors.lastname: Zhou
authors.affiliation: Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands.
authors.forename: Matthijs M
authors.initials: MM
authors.lastname: Jore
authors.affiliation: Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands.
authors.forename: Stan J J
authors.initials: SJJ
authors.lastname: Brouns
authors.affiliation: Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, The Netherlands.
authors.forename: John
authors.initials: J
authors.lastname: van der Oost
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA.|Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.|Department of Chemistry, University of California, Berkeley, California 94720, USA.|Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Doudna
authors.affiliation: Howard Hughes Medical Institute, University of California, Berkeley, California 94720, USA.|Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.|Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Eva
authors.initials: E
authors.lastname: Nogales
mesh_terms: D020029:Base Pairing; D020285:Cryoelectron Microscopy; D048168:Escherichia coli K12 / Q000737:chemistry / Q000235:genetics* / Q000276:immunology* / Q000821:virology; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000276:immunology / Q000648:ultrastructure*; D055029:Inverted Repeat Sequences / Q000235:genetics / Q000276:immunology; D046911:Macromolecular Substances / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*; D008954:Models, Biological; D008958:Models, Molecular; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000235:genetics / Q000276:immunology* / Q000648:ultrastructure*
chemical_list: D029968:Escherichia coli Proteins; D046911:Macromolecular Substances; D012329:RNA, Bacterial