Reactome: A Curated Pathway Database

Lariat Formation and 5'-Splice Site Cleavage

Stable Identifier
R-HSA-72143
Type
Reaction
Species
Homo sapiens
Compartment
Synonyms
First step of mRNA splicing
Locations in the PathwayBrowser
Summation

In the first catalytic step of mRNA splicing, the 2' OH group of the bulged A at the branch site performs a nucleophilic attack on the 5' splice site phosphodiester bond, resulting in cleavage of the bond between the 5' exon and the 5' end of the intron, and formation of a new bond between the 5' end of the intron and the branch site A. This results in a lariat-shaped intermediate, with the intron still attached to the 3' exon. The branch site A has a 2'-5' phosphodiester bond with the G at the beginning of the intron, in addition to the usual 5'-3' and 3'-5'phosphodiester bonds.

Literature References
Participants
Participant Of
Orthologous Events