present in the euglenoids, which branched from the same common ancestor as the kinetoplastids. In the protozoan Leishmania tarentolae, 12 of the 18 mitochondrial genes are edited using this process. One such gene is Cyb. The mRNA is actually edited twice in succession. For the first edit, the relevant sequence on the mRNA is as follows: mRNA 5' AAAGAAAAGGCUUUAACUUCAGGUUGU 3' The 3' end is used to anchor the gRNA (gCyb-I gRNA in this case) by basepairing (some G/U pairs are used). The 5' end does not exactly match and one of three specific endonucleases cleaves the mRNA at the mismatch site. gRNA 3' AAUAAUAAAUUUUUAAAUAUAAUAGAAAAUUGAAGUUCAGUA 5' mRNA 5' A A AGAAA A G G C UUUAACUUCAGGUUGU 3' The mRNA is now "repaired" by adding U's at each editing site in succession, giving the following 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) Guide RNA in Prokaryotes CRISPR In Prokaryotes The majority of prokaryotes, which encompass bacteria and archaea, use CRISPR (clustered regularly interspaced short palindromic repeats) with its associated Cas enzymes, as their adaptive immune system. When prokaryotes are infected by phages, and manage to fend off the attack, specific Cas enzymes will cut the phage DNA (or RNA) and integrate the parts in between the repeats of the CRISPR sequence. The stored segments can then be recognized in future virus attacks and Cas enzymes will use RNA copies of them, together with their associated CRISPR segments, as gRNA to identify the foreign sequences and render them harmless. Structure Guide RNA targets the complementary sequences by simple Watson-Crick base pairing. In type II CRISPR/cas system, single guide RNA (sgRNA) directs the target specific regions. Single guide RNA are artificially programmed combination of two RNA molecules, one component (tracrRNA) is responsible for Cas9 endonuclease activity and other (crRNA) binds to the target specific DNA region. Therefore, the trans activating RNA (tracrRNA) and crRNA are two key components and are joined by tetraloop which results in formation of sgRNA. TracrRNA are base pairs having a stem loop structure in itself and attaches to the endonuclease enzyme. Transcription of CRISPR locus gives CRISPR RNA (crRNA) which have spacer flanked region due to repeat sequences, consisting of 18-20 base pair. crRNA identifies the specific complementary target region which is cleaved