title: DNA Targeting by a Minimal CRISPR RNA-Guided Cascade.
abstract: Bacteria employ surveillance complexes guided by CRISPR (clustered, regularly interspaced, short palindromic repeats) RNAs (crRNAs) to target foreign nucleic acids for destruction. Although most type I and type III CRISPR systems require four or more distinct proteins to form multi-subunit surveillance complexes, the type I-C systems use just three proteins to achieve crRNA maturation and double-stranded DNA target recognition. We show that each protein plays multiple functional and structural roles: Cas5c cleaves pre-crRNAs and recruits Cas7 to position the RNA guide for DNA binding and unwinding by Cas8c. Cryoelectron microscopy reconstructions of free and DNA-bound forms of the Cascade/I-C surveillance complex reveal conformational changes that enable R-loop formation with distinct positioning of each DNA strand. This streamlined type I-C system explains how CRISPR pathways can evolve compact structures that retain full functionality as RNA-guided DNA capture platforms.
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors: Megan L
authors: ML
authors: Hochstrasser
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: dtaylor@utexas.edu.
authors: David W
authors: DW
authors: Taylor
authors: Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
authors: Jack E
authors: JE
authors: Kornfeld
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors: Eva
authors: E
authors: Nogales
authors: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: doudna@berkeley.edu.
authors: Jennifer A
authors: JA
authors: Doudna
mesh_terms: D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D064113:CRISPR-Cas Systems; D003001:Cloning, Molecular; D020285:Cryoelectron Microscopy; D004247:DNA / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016969:Desulfovibrio vulgaris / Q000235:genetics* / Q000378:metabolism; D004720:Endonucleases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D000072669:Gene Editing; D015870:Gene Expression; D007700:Kinetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009876:Operon; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000094704:RNA, Guide, CRISPR-Cas Systems / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D012329:RNA, Bacterial; D000094704:RNA, Guide, CRISPR-Cas Systems; D011994:Recombinant Proteins; D004247:DNA; D004720:Endonucleases