Chapter 23 Catalytic RNA 莘大
Chapter 23 Catalytic RNA
23.1 Introduction 23.2 Group I introns undertake self-splicing by transesterification 23. 3 Group I introns form a characteristic secondary structure 23. 4 Ribozymes have various catalytic activities 23.5 Some introns code for proteins that sponsor mobility 23. 6 The catalytic activity of RNAase P is due to rna 23. 7 Viroids have catalytic activity 23. 8 RNA editing occurs at individual bases 23 9 RNA editing can be directed by guide rnas 消当
23.1 Introduction 23.2 Group I introns undertake self-splicing by transesterification 23.3 Group I introns form a characteristic secondary structure 23.4 Ribozymes have various catalytic activities 23.5 Some introns code for proteins that sponsor mobility 23.6 The catalytic activity of RNAase P is due to RNA 23.7 Viroids have catalytic activity 23.8 RNA editing occurs at individual bases 23.9 RNA editing can be directed by guide RNAs
23.1Introduction The idea that only proteins have enzymatic activity was deeply rooted in biochemistry The enzyme ribonuclease P is a ribonucleoprotein that contains a single RNa molecule bound to a protein Small rnas of the virusoid class have the ability to perform a self-cleavage reaction Introns of the group I and group il classes possess the ability to splice themselves out of the pre-mRNa that contains them 消当
The idea that only proteins have enzymatic activity was deeply rooted in biochemistry. The enzyme ribonuclease P is a ribonucleoprotein that contains a single RNA molecule bound to a protein. Small RNAs of the virusoid class have the ability to perform a self-cleavage reaction. Introns of the group I and group II classes possess the ability to splice themselves out of the pre-mRNA that contains them. 23.1 Introduction
23.1Introduction The common theme of these reactions is that the RNA can perform an intramolecular or intermolecular reaction that involves cleavage or joining of phosphodiester bonds in vitro RNA Splicing is not the only means by which changes can be introduced in the informational content of rna 消当
The common theme of these reactions is that the RNA can perform an intramolecular or intermolecular reaction that involves cleavage or joining of phosphodiester bonds in vitro. RNA splicing is not the only means by which changes can be introduced in the informational content of RNA. 23.1 Introduction
23.2 Group I introns undertake self- splicing by transesterification Exon 1 Intron Exon 2 Figure 23. 1 Splicing of the Tetrahymena 35S rRNA precursor Gel electrophoresis Transcript can be followed by gel 35S RNA electrophoresis. The removal of the intron is revealed by the Splicing appearance of a rapidly moving small band. When the intron becomes circular. it Cyclization electrophoreses more slowly, as seen by a higher band Circular intron unear intron 消当
Figure 23.1 Splicing of the Tetrahymena 35S rRNA precursor can be followed by gel electrophoresis. The removal of the intron is revealed by the appearance of a rapidly moving small band. When the intron becomes circular, it electrophoreses more slowly, as seen by a higher band. 23.2 Group I introns undertake selfsplicing by transesterification
23.2 Group I introns undertake self- splicing by transesterification 3-oH end of G attacks Figure 23.2 Self-splicing-com5S2tme occurs by transesterification pGpxpxpXpXpXpX reactions in which bonds Second transfer are exchanged directly The bonds that have been generated at each stage are indicated by Third transfer the shaded boxes 消当
Figure 23.2 Self-splicing occurs by transesterification reactions in which bonds are exchanged directly. The bonds that have been generated at each stage are indicated by the shaded boxes. 23.2 Group I introns undertake selfsplicing by transesterification
3-OH ofG attacks pA or pl OG. UUUpACCUpUUG 5G.. UUUpAC CUpUUG 23.2 Group I OH introns undertake self-splicing by Cyclization GpUUG transesterification Reverse cyclization Figure 23.3 The excised intron can form circles by pUG using either of two internal Lineanzation sites for reaction with the 5 end, and can reopen the L15 RNA L-19 RNA trans reaction circles by reaction with 1416 UG JUpACCUpUUC water or oligonucleotides 消当
Figure 23.3 The excised intron can form circles by using either of two internal sites for reaction with the 5 end, and can reopen the circles by reaction with water or oligonucleotides. 23.2 Group I introns undertake self-splicing by transesterification
23.2 Group I introns 3"G-0H undertake self- /Gs pairs with site near 5 5 end Of RNA splicing by transesterification G-OH attac 6'pCCCCC-OH 3' Cpc bond 5 Figure 23. 8 The L-19 linear HO-CCC RNA can bind C in the C is transferred to substrate-binding site the C-OH 3-G.C413 released reactiveG-oh 3 end is located in the G-binding site Another Cs binds and catalyzes transfer reactions 6IpCCCCc-OH 3 transfer reacton 5 is reversed that convert 2 C5 HO-CCCCCCp oligonucleotides into a C4 and 3G-OH a c6 oligonucleotide C6 is released generating L-19 RNA 请莘大 GGGAGS.5
Figure 23.8 The L-19 linear RNA can bind C in the substrate-binding site; the reactive G-OH 3 end is located in the G-binding site, and catalyzes transfer reactions that convert 2 C5 oligonucleotides into a C4 and a C6 oligonucleotide. 23.2 Group I introns undertake selfsplicing by transesterification
23.3 Group I introns form a characteristic secondary structure G-OH Figure 23. 4 Group I introns have a 5′ CUCUCU 5' UGCGGG B 3'GGGAGG transfer 3 ACGCCC common secondary structure that is IGS Q formed by 9 base paired regions The sequences of regions P4 and P7 are conserved, and identify the P4 P3 individual sequence elements P, Q, Exon 1 P7 R, and S. Pl is created by pairing Exon 2 between the end of the left exon and the igs of the intron; a region between P7 and P9 pairs with the 3 5 UAGUC 3 2 bp fom 3 AUCAG 5 at 3'end end of the intron R of intron 消当
Figure 23.4 Group I introns have a common secondary structure that is formed by 9 base paired regions. The sequences of regions P4 and P7 are conserved, and identify the individual sequence elements P, Q, R, and S. P1 is created by pairing between the end of the left exon and the IGS of the intron; a region between P7 and P9 pairs with the 3' end of the intron. 23.3 Group I introns form a characteristic secondary structure
23.3 Group I introns form a characteristic secondary structure ntron in serted in co don 10 Figure 23.5 Placing the Promoter Tetrahymena intron within the AUG B-galactosida galactosidase codon co dons Intron codons b-galactoSidase coding sequence creates an assay for self-splicing in E coli. Synthesis ofb Transcription galactosidase can be tested by Splicing adding a compound that is turned blue by the enzyme. The Translation sequence is carried by a B-gala ctosidase bacteriophage, so the presence of blue plaques indicates successful splicing Blue plaques generate d by staining for阝 galacto sidase 消当
Figure 23.5 Placing the Tetrahymena intron within the b-galactosidase coding sequence creates an assay for self-splicing in E. coli. Synthesis of bgalactosidase can be tested by adding a compound that is turned blue by the enzyme. The sequence is carried by a bacteriophage, so the presence of blue plaques indicates successful splicing. 23.3 Group I introns form a characteristic secondary structure
