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Bacteria and archaea are susceptible to viral infections just like eukaryotes; therefore, they have developed a unique adaptive immune system to protect themselves. Clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas) are present in more than 45% of known bacteria and 90% of known archaea.
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Genome editing technologies allow scientists to modify an organism’s DNA via the addition, removal, or rearrangement of genetic material at specific genomic locations. These types of techniques could potentially be used to cure genetic disorders such as hemophilia and sickle cell anemia. One popular and widely used DNA-editing research tool that could lead to safe and effective cures for genetic disorders is the CRISPR-Cas9 system. CRISPR-Cas9 stands for Clustered Regularly Interspaced...
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Type III CRISPR-Cas Immunity: Major Differences Brushed Aside.

Gintautas Tamulaitis1, Česlovas Venclovas1, Virginijus Siksnys1

  • 1Institute of Biotechnology, Vilnius University, Saulėtekio av. 7, Vilnius 10257, Lithuania.

Trends in Microbiology
|October 25, 2016
PubMed
Summary

Type III CRISPR-Cas systems are RNA-activated DNA nucleases, resolving a long-standing immunity mechanism inconsistency. They degrade invading DNA by cleaving RNA transcripts, a process crucial for bacterial defense.

Keywords:
CRISPR-CasCmrCsmautoimmunityeffector complextarget RNA-activated DNA degradation

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Type III CRISPR-Cas systems provide immunity against foreign nucleic acids.
  • Previous studies showed conflicting mechanisms for Type III-A (DNA targeting) and Type III-B (RNA targeting) complexes.

Purpose of the Study:

  • To resolve the conflicting mechanisms of Type III CRISPR-Cas systems.
  • To elucidate the dual nuclease activity and RNA-dependent DNA targeting.

Main Methods:

  • Biochemical assays to characterize Csm and Cmr complex activities.
  • Analysis of RNA-DNA interactions and base-pairing potential.

Main Results:

  • Type III CRISPR-Cas systems function as RNases and RNA-activated DNA nucleases.
  • Immunity is achieved by coupling RNA transcript cleavage to invading DNA degradation.
  • The 5'-handle of CRISPR RNA (crRNA) is critical for self/non-self discrimination.

Conclusions:

  • The mechanism of Type III CRISPR-Cas immunity involves coordinated RNA and DNA targeting.
  • Further research is needed to fully understand the detailed mechanism of nucleic acid discrimination.