Guide RNA
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Guide RNA (gRNA) is a type of RNA that is used in mRNA editing.
[edit] Overview of gRNA-mediated editing
The mitochondria for some trypanosome protozoa undergo gRNA-mediated mRNA editing. The gRNA identifies particular sequences and inserts or deletes Uridine (U) nucleotides. The edited portion of the mRNA is in the coding region, which has the effect of modifying the protein that is produced.
[edit] Example of gRNA-mediated editing
In the protozoan, Leishmania tarentolae, some mitochondrial genes are edited using this process. One such gene is Cyb.[1] While the exact sequence of events is still under study, one model has that the mRNA is actually edited twice in succession. For the first edit, the relevant sequence on the mRNA is
mRNA 5' AAAGAAAAGGCUUUAACUUCAGGUUGU 3'
The 3' end is used to anchor the gRNA (gCyb-I gRNA in this case) with normal basepairing (some G/U pairs are used). The 5' end does not exactly match and an endonuclease makes cuts in the mRNA to allow for alignment.
gRNA 3' AAUAAUAAAUUUUUAAAUAUAAUAGAAAAUUGAAGUUCAGUA 5' mRNA 5' A A AGAAA A G G C UUUAACUUCAGGUUGU 3'
The mRNA is now "repaired" by adding U, giving the sequence
gRNA 3' AAUAAUAAAUUUUUAAAUAUAAUAGAAAAUUGAAGUUCAGUA 5' mRNA 5' UUAUUAUUUAGAAAUUUAUGUUGUCUUUUAACUUCAGGUUGU 3'
This particular gene has two overlapping gRNA editing sites. The 5' end of this section is the 3' anchor for another gRNA (gCyb-II gRNA).
[edit] Notes
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