I need some help about Crispr / Cas9. The CRISPR/Cas9 technic consists (for bacterias) in "cut" bacteriophage's DNA, in order to make it unfunctional. When the RNA is transcribed (RNA which is complementary to the bacteriophage's DNA), it will be associated with crRNA and tracrRNA to form the sgRNA (single guide RNA). But I would like to know where crRNA and tracrRNA are from? and what are their function(s)/ goal(s).

Sorry If I made mistakes I'm French.

  • $\begingroup$ Note that the sgRNA is not present in the natural CIRSPR system and is only used in engineering as a replacement for both the crRNA and the tracrRNA. $\endgroup$
    – Nicolai
    Jun 12, 2017 at 10:14

1 Answer 1


I have also been wondering the same thing for a while now and I think that the best answer that I could find after reading several review papers on CRISPR/Cas9 and online information, points to tracrRNA as serving the role of multiplexing with pre-crRNA which helps pre-crRNA mature to crRNA. This process activates the crRNA. I'm not exactly sure how this multiplexing action "matures" the pre-crRNA or what exactly that even means, but that is as much insight as the literature provides (see e.g. this abstract to a conference talk).

There most likely are some more important functions that have not yet been discovered for tracrRNA yet.

  • $\begingroup$ Welcome to Biology.SE and thank you for your answer. Could you please also add the references to the review papers and online information you are mentioning? Thanks! $\endgroup$ Jun 12, 2017 at 10:08

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