xon bren I Exam2余ton2om3nnEo0年mto(n5 22.1 Introduction WNF A i Figure 22.2 RNA is modified in the nucleus by Endd'modrfication additions to the5￠and3￠ ends and by splicing to remove the introns. The NUCLEUS splicing event requires breakage of the exon-intron ransport junctions and joining of the ends of the exons the Transation: CYTOPLASM expanded illustration shows the principle schematically but not the actual order of exon events. Mature mRNA is Exon-intron junctions are b ken transported through nuclear pores to the cytoplasm. Exons are joined where it is translated 请莘大Figure 22.2 RNA is modified in the nucleus by additions to the 5￠ and 3￠ ends and by splicing to remove the introns. The splicing event requires breakage of the exon-intron junctions and joining of the ends of the exons; the expanded illustration shows the principle schematically, but not the actual order of events. Mature mRNA is transported through nuclear pores to the cytoplasm, where it is translated. 22.1 Introduction