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