Group 1 introns, self-splicing

Another X-ray crystallographic structure, at 3.1-A resolution, of the purple bacterium Azoarcus sp. group I self-splicing intron was published in 2004 by... 

Karbstein, K., Lee, J., and Herschlag, D. (2007). Probing the role of a secondary structure element at the 5 - and splice sites in group I intron self-splicing The Tetrahymena L-16ScaI ribozyme reveals a new role for the G U pair in self-splicing. Biochemistry 46, 4861-4875. 

Analysis of Divalent Metal Ion Interactions in the Group I Self-Splicing Intron Active Site... 

Sontheimer El, Gordon PM, Piccirilli lA. Metal ion catalysis during group II intron self-splicing parallels with the spliceosome. Genes. Dev. 1999 13 1729-1741. 

The similarity In the mechanisms of group II intron self-splicing and spliceosomal splicing of pre-mRNAs also... 

The snRNAs In the spliceosome are thought to have an overall tertiary structure similar to that of group II self-splicing Introns. 

What are the mechanistic similarities between Group II Intron self-splicing and spllceosomal splicing What is the evidence that there may be an evolutionary relationship between the two ... 

Schematic drawing showing the two transesterification steps of group I self-splicing. In the first step there is a nucleophilic attack by the guanosine cofactor on the phosphodiester bond at the 5 boundary of the intron. In the second transesterification, the free 3 hydroxyl attacks the phosphodiester bond at the downstream intron-exon border, thus causing the release of the intron as a linear RNA fragment and the covalent linkage of the two exons.

Group II intron self-splicing utilizes an adenylate residue located in the intron as the nucleophile in the first transesterification step. In both group I and group II self-splicing reactions, the upstream exon-intron boundary is cleaved first and then the 30 OH of the upstream exon carries out a nucleophilic attack on the downstream exon. 

What is mechanistically similar between group II intron self-splicing and spliceosome-mediated hnRNA splicing ... 

Contrast the group 1 and group 11 self-splicing introns. Compare spliceosome-catalyzed splicing with self-splicing. 

The discovery of self-splicing introns showed that RNA could catalyse chemical reactions. Yet, unlike proteins, RNA has no functional groups with pKa values and chemical properties similar to those considered to be important in protein-based enzymes. Steitz and Steitz (1993) postulated that two metal ions were essential for catalysis by ribozymes using a mechanism similar to DNA cleavage, in which a free 3 OH is produced. They proposed,... 

Figure 6.7 A bacterial self-splicing group I intron with both exons (PDB 1U6B). Visualized using CambridgeSoft Chem3D Ultra 10.0 with notations in ChemDraw Ultra 10.0.(Printed with permission of CambridgeSoft Corporation.) (See color plate)...

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