Presentation 10-9-14-11

Presentation 10-9-14-11 - Presentation 10 Catalytic RNA...

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Presentation 10 Catalytic RNA Lewin’s Genes X Chapter 23 ribozyme – An RNA that has catalytic activity. RNA editing – A change of sequence at the level of RNA following transcription. Protein splicing is catalyzed by the intein. 1 Ribozyme has become a general term used to describe an RNA with catalytic activity. Introns of the group I and group II classes possess the ability to splice themselves out of the RNAs that contain them. Self-splicing Tetrahymena thermophila - a free living freshwater ciliate protozoan Professor Sidney Altman, Yale University “RNAse P” Professor Thomas Cech, University of Colorado For their discovery of catalytic properties of RNA
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Group I Introns Undertake Self-Splicing by Transesterification The only factors required for autosplicing (or self-splicing ) in vitro by group I introns are two metal ions and a guanosine nucleotide. FIGURE 23.1: Splicing of the Tetrahymena 35S rRNA precursor can be followed by gel electrophoresis When the precursor rRNA is incubated in vitro , Splicing occurs as an autonomous reaction The linear 400 base intron accumulates And is converted to a circle 2 Group I Introns rRNA genes of T. thermophila and Physarum polycepalum (slime mold) Genes of fungal mitochondria 3 genes of T4 bacteriophage
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Group I Introns Undertake Self-Splicing by Transesterification FIGURE 23.2: Self-splicing occurs by transesterification reactions 3 In the frst transesterifcation: The 3 ˄ –OH end oF the guanine coFactor attacks the 5 ˄ end oF the intron In the second transesterifcation: The 3 ˄ –OH end generated at the end oF the frst exon attacks the junction between the intron and second exon. The intron is released as a linear molecule that circularizes when its 3 ˄ –OH terminus attacks a bond at one oF two internal positions.
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Group I Introns Undertake Self- Splicing by Transesterification In Tetrahymena , an internal bond of the excised intron can also be attacked by other nucleotides in a trans - splicing region. 4 FIGURE 23.3: The excised intron has catalytic activities
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Group I Introns Form a Characteristic Secondary Structure Group I introns form a secondary structure with nine duplex regions. The cores of regions P3, P4, P6, and P7 have catalytic activity.
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This note was uploaded on 09/25/2011 for the course GEN 409 taught by Professor Linda during the Spring '09 term at Iowa State.

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Presentation 10-9-14-11 - Presentation 10 Catalytic RNA...

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