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Nat Microbiol. 2017 Mar 20;2:17034. doi: 10.1038/nmicrobiol.2017.34.

Guide-independent DNA cleavage by archaeal Argonaute from Methanocaldococcus jannaschii.

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Department of Microbiology &Archaea Centre, University of Regensburg, Regensburg 93053, Germany.
Institute for Structural and Molecular Biology, Division of Biosciences, University College London, London WC1E 6BT, UK.
Molecular Biology of Archaea, Institute of Biology II, University of Freiburg, Microbiology, Schaenzlestraße 1, 79104 Freiburg, Germany.
Institute of Physical and Theoretical Chemistry - NanoBioSciences, Technische Universität Braunschweig-BRICS, Rebenring 56, 38106 Braunschweig, Germany.
Center for Integrated Protein Science Munich CIPSM, Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, 85748 Garching, Germany.
Biocentre of the LMU Munich, Department Biology I - Plant Development, Großhadernerstraße 2-4, 82152 Planegg-Martinstried, Germany.


Prokaryotic Argonaute proteins acquire guide strands derived from invading or mobile genetic elements, via an unknown pathway, to direct guide-dependent cleavage of foreign DNA. Here, we report that Argonaute from the archaeal organism Methanocaldococcus jannaschii (MjAgo) possesses two modes of action: the canonical guide-dependent endonuclease activity and a non-guided DNA endonuclease activity. The latter allows MjAgo to process long double-stranded DNAs, including circular plasmid DNAs and genomic DNAs. Degradation of substrates in a guide-independent fashion primes MjAgo for subsequent rounds of DNA cleavage. Chromatinized genomic DNA is resistant to MjAgo degradation, and recombinant histones protect DNA from cleavage in vitro. Mutational analysis shows that key residues important for guide-dependent target processing are also involved in guide-independent MjAgo function. This is the first characterization of guide-independent cleavage activity for an Argonaute protein potentially serving as a guide biogenesis pathway in a prokaryotic system.

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