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The Adaptive Immune System of Haloferax volcanii.

Maier LK, Dyall-Smith M, Marchfelder A - Life (Basel) (2015)

Bottom Line: To fight off invading genetic elements, prokaryotes have developed an elaborate defence system that is both adaptable and heritable-the CRISPR-Cas system (CRISPR is short for: clustered regularly interspaced short palindromic repeats and Cas: CRISPR associated).A systematic search revealed that six protospacer adjacent motif (PAM) sequences are recognised by the Haloferax defence system.For successful invader recognition, a non-contiguous seed sequence of 10 base-pairs between the crRNA and the invader is required.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology II, Ulm University, 89069 Ulm, Germany. lisa-katharina.maier@uni-ulm.de.

ABSTRACT
To fight off invading genetic elements, prokaryotes have developed an elaborate defence system that is both adaptable and heritable-the CRISPR-Cas system (CRISPR is short for: clustered regularly interspaced short palindromic repeats and Cas: CRISPR associated). Comprised of proteins and multiple small RNAs, this prokaryotic defence system is present in 90% of archaeal and 40% of bacterial species, and enables foreign intruders to be eliminated in a sequence-specific manner. There are three major types (I-III) and at least 14 subtypes of this system, with only some of the subtypes having been analysed in detail, and many aspects of the defence reaction remaining to be elucidated. Few archaeal examples have so far been analysed. Here we summarize the characteristics of the CRISPR-Cas system of Haloferax volcanii, an extremely halophilic archaeon originally isolated from the Dead Sea. It carries a single CRISPR-Cas system of type I-B, with a Cascade like complex composed of Cas proteins Cas5, Cas6b and Cas7. Cas6b is essential for CRISPR RNA (crRNA) maturation but is otherwise not required for the defence reaction. A systematic search revealed that six protospacer adjacent motif (PAM) sequences are recognised by the Haloferax defence system. For successful invader recognition, a non-contiguous seed sequence of 10 base-pairs between the crRNA and the invader is required.

No MeSH data available.


Acquisition of new spacers. The invader DNA is degraded by Cas proteins and a piece of the invader DNA is integrated as a new spacer (shown as red rectangle) into the CRISPR locus. Repeats are shown as diamonds, spacers as grey rectangles and the leader region as white rectangle. The leader is located at the 5' end of the CRISPR locus. The CRISPR locus including the novel spacer is shown at the right, the original CRISPR locus is shown at the left. The invader DNA to which Cas1 and Cas2 bind is shown at the bottom.
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life-05-00521-f001: Acquisition of new spacers. The invader DNA is degraded by Cas proteins and a piece of the invader DNA is integrated as a new spacer (shown as red rectangle) into the CRISPR locus. Repeats are shown as diamonds, spacers as grey rectangles and the leader region as white rectangle. The leader is located at the 5' end of the CRISPR locus. The CRISPR locus including the novel spacer is shown at the right, the original CRISPR locus is shown at the left. The invader DNA to which Cas1 and Cas2 bind is shown at the bottom.

Mentions: The CRISPR-Cas system is the most elaborate defence strategy present in prokaryotic cells (for general reviews about the CRISPR-Cas system see: [1,2,3,4,5,6,7,8,9]). It confers immunity against foreign genetic elements by a sequence-specific targeting and elimination of the invading nucleic acids. To this end, the cell establishes and maintains a genetic record of previously encountered viruses and plasmids within its CRISPR loci. These genomic regions are arrays of recurring repeat sequences, between which are short variable spacer sequences that represent genetic samples of invader DNA [10,11]. CRISPR loci not only provide genetically heritable systems for specific immunity but also, by their transcription, give rise to a key player of CRISPR defence, the crRNA. In proximity to CRISPR loci are gene cassettes encoding Cas proteins, that are responsible for all parts of the defence reaction: acquisition of foreign DNA (spacer sequences), crRNA biogenesis as well as target degradation. The defence reaction progresses in three stages. In the first stage, new spacer sequences are acquired. Here, as shown in Figure 1, a short piece of invader nucleic acid is selected and integrated into a CRISPR locus [5,7]. For this step, type I and II systems require short sequence motifs, called PAMs [12,13]. These motifs are part of the invader DNA and are used by the adaptation machinery for selecting the invader DNA fragment to be integrated. In addition, they are essential for the recognition and degradation of the invader upon a recurring infection.


The Adaptive Immune System of Haloferax volcanii.

Maier LK, Dyall-Smith M, Marchfelder A - Life (Basel) (2015)

Acquisition of new spacers. The invader DNA is degraded by Cas proteins and a piece of the invader DNA is integrated as a new spacer (shown as red rectangle) into the CRISPR locus. Repeats are shown as diamonds, spacers as grey rectangles and the leader region as white rectangle. The leader is located at the 5' end of the CRISPR locus. The CRISPR locus including the novel spacer is shown at the right, the original CRISPR locus is shown at the left. The invader DNA to which Cas1 and Cas2 bind is shown at the bottom.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390866&req=5

life-05-00521-f001: Acquisition of new spacers. The invader DNA is degraded by Cas proteins and a piece of the invader DNA is integrated as a new spacer (shown as red rectangle) into the CRISPR locus. Repeats are shown as diamonds, spacers as grey rectangles and the leader region as white rectangle. The leader is located at the 5' end of the CRISPR locus. The CRISPR locus including the novel spacer is shown at the right, the original CRISPR locus is shown at the left. The invader DNA to which Cas1 and Cas2 bind is shown at the bottom.
Mentions: The CRISPR-Cas system is the most elaborate defence strategy present in prokaryotic cells (for general reviews about the CRISPR-Cas system see: [1,2,3,4,5,6,7,8,9]). It confers immunity against foreign genetic elements by a sequence-specific targeting and elimination of the invading nucleic acids. To this end, the cell establishes and maintains a genetic record of previously encountered viruses and plasmids within its CRISPR loci. These genomic regions are arrays of recurring repeat sequences, between which are short variable spacer sequences that represent genetic samples of invader DNA [10,11]. CRISPR loci not only provide genetically heritable systems for specific immunity but also, by their transcription, give rise to a key player of CRISPR defence, the crRNA. In proximity to CRISPR loci are gene cassettes encoding Cas proteins, that are responsible for all parts of the defence reaction: acquisition of foreign DNA (spacer sequences), crRNA biogenesis as well as target degradation. The defence reaction progresses in three stages. In the first stage, new spacer sequences are acquired. Here, as shown in Figure 1, a short piece of invader nucleic acid is selected and integrated into a CRISPR locus [5,7]. For this step, type I and II systems require short sequence motifs, called PAMs [12,13]. These motifs are part of the invader DNA and are used by the adaptation machinery for selecting the invader DNA fragment to be integrated. In addition, they are essential for the recognition and degradation of the invader upon a recurring infection.

Bottom Line: To fight off invading genetic elements, prokaryotes have developed an elaborate defence system that is both adaptable and heritable-the CRISPR-Cas system (CRISPR is short for: clustered regularly interspaced short palindromic repeats and Cas: CRISPR associated).A systematic search revealed that six protospacer adjacent motif (PAM) sequences are recognised by the Haloferax defence system.For successful invader recognition, a non-contiguous seed sequence of 10 base-pairs between the crRNA and the invader is required.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology II, Ulm University, 89069 Ulm, Germany. lisa-katharina.maier@uni-ulm.de.

ABSTRACT
To fight off invading genetic elements, prokaryotes have developed an elaborate defence system that is both adaptable and heritable-the CRISPR-Cas system (CRISPR is short for: clustered regularly interspaced short palindromic repeats and Cas: CRISPR associated). Comprised of proteins and multiple small RNAs, this prokaryotic defence system is present in 90% of archaeal and 40% of bacterial species, and enables foreign intruders to be eliminated in a sequence-specific manner. There are three major types (I-III) and at least 14 subtypes of this system, with only some of the subtypes having been analysed in detail, and many aspects of the defence reaction remaining to be elucidated. Few archaeal examples have so far been analysed. Here we summarize the characteristics of the CRISPR-Cas system of Haloferax volcanii, an extremely halophilic archaeon originally isolated from the Dead Sea. It carries a single CRISPR-Cas system of type I-B, with a Cascade like complex composed of Cas proteins Cas5, Cas6b and Cas7. Cas6b is essential for CRISPR RNA (crRNA) maturation but is otherwise not required for the defence reaction. A systematic search revealed that six protospacer adjacent motif (PAM) sequences are recognised by the Haloferax defence system. For successful invader recognition, a non-contiguous seed sequence of 10 base-pairs between the crRNA and the invader is required.

No MeSH data available.