22.4 The spliceosome Nuclear splicing constructs an active site from pairing between U6-02 and U2-intron contains snrnas Figure 22 17 Nuclear ccCCUU splicing and group UGAUC? splicing involve the L UGUAGUA formation of similar sexn2G具 A CA UCAL secondary structures The sequences are more exon 1--G U Group II splicing constructs an active center specific in nuclear from the base paired reg ons of domains 5 and 6 splicing, group II corrin RAGCNNNB O splicing uses positions Y UUGNNNYN that may be occupied by 3"Eexn2Y具 dormain b either purine(r)or 闭筝大 leither pyrimidine(Y) exon 1--G UFigure 22.17 Nuclear splicing and group II splicing involve the formation of similar secondary structures. The sequences are more specific in nuclear splicing; group II splicing uses positions that may be occupied by either purine (R) or either pyrimidine (Y). 22.4 The spliceosome contains snRNAs