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Mechanism of spacer integration links the CRISPR/Cas system to transposition as a form of mobile DNA.

Dyda F, Hickman AB - Mob DNA (2015)

Bottom Line: These are typified by multiple copies of DNA sequences known as clustered regularly interspaced short palindromic repeats (CRISPRs).These CRISPR repeats are the sites at which short spacers containing sequences of previously encountered foreign DNA are integrated, and the spacers serve as the molecular memory of previous invaders.In vivo work has demonstrated that two CRISPR-associated proteins - Cas1 and Cas2 - are required for spacer integration, but the mechanism by which this is accomplished remained unclear.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 5 Center Dr., Bethesda, MD 20892 USA.

ABSTRACT
It has recently become clear that many bacterial and archaeal species possess adaptive immune systems. These are typified by multiple copies of DNA sequences known as clustered regularly interspaced short palindromic repeats (CRISPRs). These CRISPR repeats are the sites at which short spacers containing sequences of previously encountered foreign DNA are integrated, and the spacers serve as the molecular memory of previous invaders. In vivo work has demonstrated that two CRISPR-associated proteins - Cas1 and Cas2 - are required for spacer integration, but the mechanism by which this is accomplished remained unclear. Here we review a recent paper describing the in vitro reconstitution of CRISPR spacer integration using purified Cas1 and Cas2 and place the results in context of similar DNA transposition reactions and the crystal structure of the Cas1/Cas2 complex.

No MeSH data available.


Related in: MedlinePlus

Overview and details of a CRISPR locus. (A) Clustered regularly interspaced short palindromic repeats (CRISPRs, in green) typically alternate with spacers of different sequence but similar length (shades of gray and black). (B) Proposed double-ended integration of a protospacer (red) into the site of a CRISPR repeat. This results in a duplication of the CRISPR. (C) Sequence and deduced cruciform structure of the E. coli 28 nt CRISPR repeat.
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Fig1: Overview and details of a CRISPR locus. (A) Clustered regularly interspaced short palindromic repeats (CRISPRs, in green) typically alternate with spacers of different sequence but similar length (shades of gray and black). (B) Proposed double-ended integration of a protospacer (red) into the site of a CRISPR repeat. This results in a duplication of the CRISPR. (C) Sequence and deduced cruciform structure of the E. coli 28 nt CRISPR repeat.

Mentions: The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system, present in approximately 90% of archaea and approximately 50% of bacteria, is an adaptive immune system (reviewed in [1]) that generates small RNAs (known as crRNAs) transcribed from chromosomally integrated foreign DNA fragments and uses them to direct the degradation of invading DNA that contains the same sequence. The foreign DNA fragments, called ‘spacers’, are integrated into a chromosomal CRISPR locus composed of an array of short palindromic repeats forming a repeat-spacer-repeat pattern (Figure 1A). Adjacent to the CRISPR locus is the several hundred base pairs long AT-rich ‘leader sequence’ preceded by the cas genes. The cas genes associated with CRISPR systems are quite variable, with over 45 different gene families identified in various organisms. Although six cas genes (cas1 to 6) are extensively conserved, only cas1 and cas2 are always present in those genomes that contain a CRISPR locus.Figure 1


Mechanism of spacer integration links the CRISPR/Cas system to transposition as a form of mobile DNA.

Dyda F, Hickman AB - Mob DNA (2015)

Overview and details of a CRISPR locus. (A) Clustered regularly interspaced short palindromic repeats (CRISPRs, in green) typically alternate with spacers of different sequence but similar length (shades of gray and black). (B) Proposed double-ended integration of a protospacer (red) into the site of a CRISPR repeat. This results in a duplication of the CRISPR. (C) Sequence and deduced cruciform structure of the E. coli 28 nt CRISPR repeat.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4940900&req=5

Fig1: Overview and details of a CRISPR locus. (A) Clustered regularly interspaced short palindromic repeats (CRISPRs, in green) typically alternate with spacers of different sequence but similar length (shades of gray and black). (B) Proposed double-ended integration of a protospacer (red) into the site of a CRISPR repeat. This results in a duplication of the CRISPR. (C) Sequence and deduced cruciform structure of the E. coli 28 nt CRISPR repeat.
Mentions: The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system, present in approximately 90% of archaea and approximately 50% of bacteria, is an adaptive immune system (reviewed in [1]) that generates small RNAs (known as crRNAs) transcribed from chromosomally integrated foreign DNA fragments and uses them to direct the degradation of invading DNA that contains the same sequence. The foreign DNA fragments, called ‘spacers’, are integrated into a chromosomal CRISPR locus composed of an array of short palindromic repeats forming a repeat-spacer-repeat pattern (Figure 1A). Adjacent to the CRISPR locus is the several hundred base pairs long AT-rich ‘leader sequence’ preceded by the cas genes. The cas genes associated with CRISPR systems are quite variable, with over 45 different gene families identified in various organisms. Although six cas genes (cas1 to 6) are extensively conserved, only cas1 and cas2 are always present in those genomes that contain a CRISPR locus.Figure 1

Bottom Line: These are typified by multiple copies of DNA sequences known as clustered regularly interspaced short palindromic repeats (CRISPRs).These CRISPR repeats are the sites at which short spacers containing sequences of previously encountered foreign DNA are integrated, and the spacers serve as the molecular memory of previous invaders.In vivo work has demonstrated that two CRISPR-associated proteins - Cas1 and Cas2 - are required for spacer integration, but the mechanism by which this is accomplished remained unclear.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 5 Center Dr., Bethesda, MD 20892 USA.

ABSTRACT
It has recently become clear that many bacterial and archaeal species possess adaptive immune systems. These are typified by multiple copies of DNA sequences known as clustered regularly interspaced short palindromic repeats (CRISPRs). These CRISPR repeats are the sites at which short spacers containing sequences of previously encountered foreign DNA are integrated, and the spacers serve as the molecular memory of previous invaders. In vivo work has demonstrated that two CRISPR-associated proteins - Cas1 and Cas2 - are required for spacer integration, but the mechanism by which this is accomplished remained unclear. Here we review a recent paper describing the in vitro reconstitution of CRISPR spacer integration using purified Cas1 and Cas2 and place the results in context of similar DNA transposition reactions and the crystal structure of the Cas1/Cas2 complex.

No MeSH data available.


Related in: MedlinePlus