What is the pre-mRNA splicing mechanism?
The exchange of U1 snRNP for U6 snRNP occurs before the first transesterification; this exchange requires the 5' splice site to be read by two different snRNPs, thereby increasing the accuracy of 5' splice site to be read by two different snRNPs, thereby increasing the accuracy of the 5' splice site selection
The branch point site is recognized by BBP and then U2; this check and recheck strategy provides icnreased accuracy of site selection.
U2 binds, forcing the appropriate adenine to be unpaired adn activated for the attack on the 5' splice site.
This, in combo with recognition by BBP is the way the spliceosome chooses the right adenine.
After the first transesterification, a series of rearrangements brings the two exons together for the second transesterification.
The snRNAs both position the reactants and provide the catalytic sites for the two reactions.
The U5 is present in the spliceosome before the rearrangement