23.2 Group I introns undertake self- splicing by transesterification fa过transter 多9的809 ttacks G-OH Figure 23.2 Self-splicing 53 5 Exon B3 pG-OH pN pNpNpN pN pNp以单XXp式p occurs by oNpNpNpNpNpN-OH transesterification pGpXpXpXpXpXpx reactions in which bonds Second transfer are exchanged directly. 8888m合aca The bonds that have been generated at each stage are indicated by Third transfer 983658a弯瓶 the shaded boxes. 情華大兰
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 of G attacks pAor pu SG.UUUPACCUPUUG 5G.UUUpACCUpUUG 23.2 Group I 414 introns undertake Cyclization self-splicing by UG transesterification Reverse cyclization Figure 23.3 The excised intron can form circles by Secondary cyclization using either of two internal OH Linearization OH sites for reaction with the 5 414 end,and can reopen the L15 RNA L19 RNA trans reaction circles by reaction with 16 20 UUUPACCUPUUG water or oligonucleotides. 清菜大当
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 -OH Cs pairs with undertake self- 595 IGS site near 5' end of RNA splicing by transesterification G-OH attacks CC-OH 3 CpC bond GGAGE-5 Figure 23.8 The L-19 linear HO-CCCCn RNA can bind C in the C is transferred to substrate-binding site;the C-OH 3'-G;C4IS GGGAGE-5 released reactive G-OH 3 end is located in the G-binding site, C-OH and catalyzes transfer reactions Another Cs binds CC-OH 3 transfer reaction is reversed that convert 2 C5 HO-CCCCCCp oligonucleotides into a C4 and C6 is released, a C6 oligonucleotide eraing.19 情菜大兰
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 Exor G-OH P Figure 23.4 Group I introns have a 5'cUcUCU First 5'UGCGGGB 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 P P3 P6 individual sequence elements P,Q. Exon P7 R,and S.PI is created by pairing Exon 2 between the end of the left exon P8 and the IGS of the intron;a region between P7 and P9 pairs with the 3 X0X8 2 bp fomm at 3'end end of the intron. R of intron 清苇大当
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 Figure 23.5 Placing the ntron inserted in codon 10 Promoter Tetrahymena intron within the AUG B-galactosidase codon codons Intron nosidase b-galactosidase coding sequence creates an assay for self-splicing 门 in E.coli.Synthesis of b- Transcription galactosidase can be tested by Splicing adding a compound that is turned blue by the enzyme.The sequence is carried by a B-galactosidase bacteriophage,so the presence of blue plaques indicates Blue plaques generated 00o successful splicing. by staining for B- galactosidase 清菜大当
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