Question

describe experiment that shows that U2 base pairs with branch
point sequence

Answer 1

Spliceosome-mediated RNA splicing mechanism. RNA splicing is catalyzed by a spliceosome formed from the assembly of U1, U2, U5 and U4/U6 snRNPs plus other components. The commitment complex initiates the process by binding of U1-snRNP, which binds to the 5’ splice site by RNA-RNA base pairing, Branch point binding protein (BBP), binds to branch point, splicing factor U2AF, binds with polypyrimidine tract and members of SR protein family. The pre-spliceosome complex comprise the commitment complex plus U2-snRNP, the latter attached to the branch site. At this stage, an association between U1-snRNP and U2-snRNP brings the 5’ splice site into the close proximity to the branch point. Spliceosome formed when U4/U6 and U5-snRNP attach to pre-spliceosome complex. After binding all the factors, U1 snRNP released. The release of U1 snRNP allows U5 snRNP to interact with 5’ splice site. The catalytic reaction is triggered by the release of U4. When U4 dissociates, U6 snRNP pair with U2 snRNP to form active site. Which helps to bring the 3’ splice site close to 5’ site and the branch point. Afterwards, two exin sequences are thereby joined to each other and intron sequence is released as a lariat.