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The Lariat capping ribozyme formerly called GIR1 branching ribozyme is a 179 nt ribozyme with an apparent resemblance to a group I ribozyme. It is found within a complex type of group I introns also termed twin-ribozyme introns. Rather than splicing, it catalyses a branching reaction in which the 2'OH of an internal residue is involved in a nucleophilic attack at a nearby phosphodiester bond. As a result, the RNA is cleaved at an internal processing site (IPS), leaving a 3'OH and a downstream product with a tiny lariat at its 5' end. The lariat has the first and the third nucleotide joined by a 2',5' phosphodiester bond and is referred to as 'the lariat cap' because it caps an intron-encoded mRNA. The resulting lariat cap seems to contribute by increasing the half-life of the HE mRNA,〔 thus conferring an evolutionary advantage to the HE. == Biological context == The GIR1 ribozyme was originally discovered during the functional characterization of the introns from the extrachromosomal rDNA of the ''Didymium iridis'' protist. A combination of deletion and ''in vitro'' self-splicing analyses revealed a twin-ribozyme intron organization: two distinct ribozyme domains within the intron.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「GIR1 branching ribozyme」の詳細全文を読む スポンサード リンク
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