Figure 2: U2-Type Spliceosome Facilitated pre-mRNA Splicing Mechanism.
Small nuclear ribonuceoprotein (snRNP) U2 facilitated spliceosome assembly begins with the U1 snRNP associating with the 5’ splice site and U2 at the branch point (complex A). The pre-assembled U4/U5/U6 tri-snRNP is recruited to form the pre-catalytic spliceosome (complex B1). U1 and U4 snRNPs are then destabilized by various protein interactions resulting in the catalytically active spliceosome (complex B2). The U2/U5/U6 spliceosome complex then facilitates intron excision and exon ligation via two step catalytic process (complex C).