UI snRNP U2 snRNP Primary ADP+P1 transcript 5 Exon sEx Gpl UI U4/U6+U5 The 3 Oh of guanosine ADP+ P OH ts as a nucleophile, attacking the phosphate at uwe Inactive the 5 splice site splIceosome U2 PGpA Intermediate ADP+P小U1,U4 Active U--OH GpU. spliceosome 5 The 3'oH of the 5'exon U6 U2 becomes the nucleophile. Lariat ompleting the reacti formation U5 5 PGpA oH 3 G-OH 3' U6 U2 U5 Spliced RNA Intron release 5 UpU 3