CRISPR-Cas9 genome editing – answers
Last time we looked at CRISPR-Cas9 genome editing and I asked a couple of questions.
- How would the bacteria be able to make a specific “guide RNA” that matches a piece of viral DNA? (Hint – how is RNA made?)
- You want to use CRISPR-Cas9 to do some genome editing. Why do you need to design the guide RNA you are going to use?
These are my answers:
- RNA is made by transcription – it is copied from DNA. So the bacteria must have bits of viral DNA in their genome. This discovery of viral DNA in a bacterial genome was what led Fransisco Mojica to guess (propose a hypothesis) that this was a type of immune system against viruses.
- The guide RNA needs to match the DNA you want to cut. So you need to find out the sequence of the DNA you’re editing and design a matching RNA sequence.
A guide RNA sequence is complementary to the DNA strand it will bind to. But note that it is the same as the opposite DNA strand, except that RNA has a U where DNA has a T.
The story of CRISPR-cas9 research:
http://www.cell.com/cell/pdf/S0092-8674(15)01705-5.pdf. This is the human story behind the discoveries, and was published in the scientific journal Cell.
https://www.broadinstitute.org/what-broad/areas-focus/project-spotlight/crispr-timeline. This is a timeline of the research. It starts with a chance observation made during basic research, and leads to using the results of research from different labs over several years for a specific purpose.