Mechanism for Group I intron splicing

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Self-splicing is a special case of splicing that occurs within the introns of some unicellular organisms. These reactions are noteworthy because splicing of Group I introns occurs in the absence of proteins, and involves two successive transesterification steps.

This intron class utilise a guanosine cofactor in catalysis that is sequestered in a globular pre-formed active site, analogous to that of a protein enzyme.

The 3'-OH of a guanosine (G, GMP, GDP, GTP all function) acts as a nucleophile, attacks the phosphate at the 5' exon-intron junction, and covalently binds to the excised intron. This step requires metal ions for folding and catalysis.

Then 3'-OH of the released 5' -exon attacks the 3' junction phosphate, completing the splice.

Exons are ligated and a free linear intron, with the G nucleoside attached at 5' end, is released. After splicing, intron acts upon itself to circularise.

Last modified: Tue Feb 10 11:13:10 CET 2004