Catalytic RNA has a guanosine-bin ding site 23.4 Ribozymes have sub strate-b inding site various catalytic Guanosine bind in CUCUC Sub strate bind activities ACC First transfer G-OH occupies G-binding site; 5 e xon occupies substrate-binding site Figure 23. 6 Excision of the group i intron in Tetrahymena IRNA occurs by successive Second transfer is in G-binding site: 5 reactions between the occupants exon is in substrate-bind ing site 5-CUCUC of the guanosine-binding site and substrate-binding site. The left ACe GAC exon is red, and the right exon is Third transfer G is in G-binding site: 5'end of intron is in sub strate-binding site purple GGGACO GGGAGG 消当 UUUACCU
Figure 23.6 Excision of the group I intron in Tetrahymena rRNA occurs by successive reactions between the occupants of the guanosine-binding site and substrate-binding site. The left exon is red, and the right exon is purple. 23.4 Ribozymes have various catalytic activities
23.4 Ribozymes have various catalytic activities -OH end ofG attacks G-OH end of int Exon A pG-OH pN pNpNpN pNpN pXpXpXpXpXpx Figure 23.2 Self-splicing pNpNpNpNpN pN-OH occurs by DGpxpXpXpXp Xpx transesterification G-P Second transfer reactions in which bonds g -oH of exon A attacks .OH end of exon are exchanged directly The bonds that have been generated at each Third transfer stage are indicated by 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. 23.4 Ribozymes have various catalytic activities