Short motif sequences determine the targets of the prokaryotic CRISPR defence system

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Title: Short motif sequences determine the targets of the prokaryotic CRISPR defence system
Authors: Mojica, Francisco J.M. | Díez-Villaseñor, César | García-Martínez, Jesús | Almendros, Cristóbal
Research Group/s: Microbiología Molecular
Center, Department or Service: Universidad de Alicante. Departamento de Fisiología, Genética y Microbiología
Keywords: PAM | Proto-spacer adjacent motif | SRSR | Short regularly spaced repeats | CRISPR | Clustered regularly interspaced short palindromic repeats | PAME | Proto-spacer adjacent motif end | CAS | CRISPR-associated sequence
Knowledge Area: Microbiología
Issue Date: 1-Mar-2009
Publisher: Microbiology Society
Citation: Microbiology. 2009, 155: 733-740. doi:10.1099/mic.0.023960-0
Abstract: Clustered regularly interspaced short palindromic repeats (CRISPR) and their associated CRISPR-associated sequence (CAS) proteins constitute a novel antiviral defence system that is widespread in prokaryotes. Repeats are separated by spacers, some of them homologous to sequences in mobile genetic elements. Although the whole process involved remains uncharacterized, it is known that new spacers are incorporated into CRISPR loci of the host during a phage challenge, conferring specific resistance against the virus. Moreover, it has been demonstrated that such interference is based on small RNAs carrying a spacer. These RNAs would guide the defence apparatus to foreign molecules carrying sequences that match the spacers. Despite this essential role, the spacer uptake mechanism has not been addressed. A first step forward came from the detection of motifs associated with spacer precursors (proto-spacers) of Streptococcus thermophilus, revealing a specific recognition of donor sequences in this species. Here we show that the conservation of proto-spacer adjacent motifs (PAMs) is a common theme for the most diverse CRISPR systems. The PAM sequence depends on the CRISPR-CAS variant, implying that there is a CRISPR-type-specific (motif-directed) choice of the spacers, which subsequently determines the interference target. PAMs also direct the orientation of spacers in the repeat arrays. Remarkably, observations based on such polarity argue against a recognition of the spacer precursors on transcript RNA molecules as a general rule.
Sponsor: This work was financed by a research grant from the Ministerio de Educación y Ciencia (BIO2004-00523).
ISSN: 1350-0872 (Print) | 1465-2080 (Online)
DOI: 10.1099/mic.0.023960-0
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2009 SGM
Peer Review: si
Publisher version:
Appears in Collections:INV - Microbiología Molecular - Artículos de Revistas

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