Mechanism for Group I intron splicing



BACK to 'Hemiascomycetous Yeast Spliceosomal Introns'

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