Intron removal from eukaryotic pre-mRNA by a spliceosome

Intron removal from eukaryotic pre-mRNA by a spliceosome. The solidus between A and G in the 5ˊ splice site (   /   ) indicates that these two nucleotides are about equally frequent in this consensus sequence. In the 3ˊ splice site, Py indicates either of the pyrimidines (   or   ) and N indicates that any nucleotide can be       Intron removal from eukaryotic pre-mRNA by a spliceosome. The solidus between A and G in the 5ˊ splice site (   /   ) indicates that these two nucleotides are about equally frequent in this consensus sequence. In the 3ˊ splice site, Py indicates either of the pyrimidines (   or   ) and N indicates that any nucleotide can be      

5’ splice Branch 3’ splice site site site Exon 1l—J—Ilntron 1[—%‘|—'—| Exon 2 5" GU‘IAGU PyNCAG-lg' ! \ @ Cleavage frees the lariat intron, and the o snRNP U1 binds 5’ splice Branch point 20—40 exons are ligated. site, and U2 binds branch adenine nucleotides site. 9 snRNPs U4, U5, and U6 Degradation bind to complex and , form the inactive spliceo- 9 The 3 end of the intron 5Exon 1 Exon 2 TI? some. A lariat intron 3 Exon 1 is cleaved. leaving a 5’ structure forms. monophosphate at the 5’ exon end. _ Lariat Lariat Exon 2 intron h 3' Intron h 3’ a U4 dissociates to form the / active spliceosome /’ . . , ' / Lariat Intron forms b a followed by 5 cleavage , o 2,_5, phosphodiestery and formation of a 2’—5’ phosphodiester bond to stabilize lariat intron. bond beween the 5’ guanine and the branch ‘0- P=O pomt adenine.