基因 Chapter 26 RNA Splicing and Processing.pdf

RNA Splicing and Processing CHAPTER OUTLINE Introduction Ul snRNP Initiates Splicing Nuclear Splice Junctions Are Short Sequences • U1 snRNP initiates splicing by binding to the 5 splice site by means of an RNA-RNA pairing reaction. • Splice sites are the sequences immediately surrounding the exon-intron boundaries. They are named for their positions • The Ecomplex contains U1 snRNP bound at the 5 splice relative to the intron. site, the protein U2AF bound to a pyrimidine tract between the branch site and the 3 splice site, and SR proteins con­ • The 5 splice site at the 5 (left) end of the intron includes the consensus sequence GU. necting U1 snRNP to U2AF. • The 3 splice site at the 3 (right) end of the intron includes The E Complex Can be Formed by Intron Definition or the consensus sequence AG. Exon Definition • The GU-AG rule (originally called the GT-AG rule in terms of • The direct way of forming an E complex is for U1 snRNP to DNA sequence) describes the requirement for these constant bind at the 5 splice site and U2AF to bind at a pyrimidine dinucleotides at the first two