Watch RecBCD, a helicase and nuclease motor protein critical to DNA repair, use torque to eject an array of mutant EcoRI in this animated trailer for Terakawa et al., "Sequencial eviction of crowded nucleoprotein complexes by the exonuclease RecBCD molecular motor", Proc Natl Acad Sci U S A. 2017 Aug 1;114(31):E6322-E6331. doi: 10.1073/pnas.1701368114.
Bacteria can become infected with viruses just like us. We have a complex immune system that defends us from invading pathogens. But bacteria lack an immune system similar to our own, so how do they protect themselves from viruses?
One way bacteria can defend themselves is by producing a special protein called Cas9, which can destroy viral DNA. But how does Cas9 find the viral DNA, and what prevents it from destroying the bacteria's own DNA? It turns out that bacteria can steal small snippets of viral DNA, and then store these stolen fragments in their own genomes like a library representing the complete history of viruses that the bacteria have been exposed to in the past. If a virus ever tries to come back, the bacteria make RNA copies of these DNA sequences. Cas9 then grabs the bits of RNA and uses them like a fingerprint to identify the viral invaders. DNA sequences matching the RNA occur only twice: once in the virus and once in the bacteria's library. So why doesn't Cas9 destroy them both? The secret lies in a short 3 letter DNA code called the PAM. The virus' DNA has a PAM in the right location, but the bacteria's DNA does not, so Cas9 uses the PAM to help it identify the virus.
In this video, we follow Cas9 as it hunts down and destroys the viral DNA with its sidekick, the strand of RNA that is complimentary to a small portion of the virus' DNA.
DNA interrogation by the CRISPR RNA-guided endonuclease Cas9. Samuel H. Sternberg, Sy Redding, Martin Jinek, Eric C. Greene, and Jennifer A. Doudna. (n.d.) Nature.doi:10.1038/nature13011
Bacteria can become infected with viruses just like us. We have a complex immune system that defends us from invading pathogens. But bacteria lack an immune system similar to our own, so how do they protect themselves from viruses?
One way bacteria can defend themselves is by producing a special protein called Cas9, which can destroy viral DNA. But how does Cas9 find the viral DNA, and what prevents it from destroying the bacteria's own DNA? It turns out that bacteria can steal small snippets of viral DNA, and then store these stolen fragments in their own genomes like a library representing the complete history of viruses that the bacteria have been exposed to in the past. If a virus ever tries to come back, the bacteria make RNA copies of these DNA sequences. Cas9 then grabs the bits of RNA and uses them like a fingerprint to identify the viral invaders. DNA sequences matching the RNA occur only twice: once in the virus and once in the bacteria's library. So why doesn't Cas9 destroy them both? The secret lies in a short 3 letter DNA code called the PAM. The virus' DNA has a PAM in the right location, but the bacteria's DNA does not, so Cas9 uses the PAM to help it identify the virus.
In this video, we follow Cas9 as it hunts down and destroys the viral DNA with its sidekick, the strand of RNA that is complimentary to a small portion of the virus' DNA.
DNA interrogation by the CRISPR RNA-guided endonuclease Cas9. Samuel H. Sternberg, Sy Redding, Martin Jinek, Eric C. Greene, and Jennifer A. Doudna. (n.d.) Nature.doi:10.1038/nature13011
An educational short produced by the Greene Lab to illustrate how proteins use different types of diffusion-based motion during the repair of mismatched DNA sequences. For more detailed information please refer to the following:
Watch RecBCD, a helicase and nuclease motor protein critical to DNA repair, use torque to eject an array of mutant EcoRI in this animated trailer for Terakawa et al., "Sequencial eviction of crowded nucleoprotein complexes by the exonuclease RecBCD molecular motor", Proc Natl Acad Sci U S A. 2017 Aug 1;114(31):E6322-E6331. doi: 10.1073/pnas.1701368114.