Commitment to splice site pairing coincides with A complex formation.
Differential recognition of exons by the spliceosome regulates gene expression and exponentially increases the complexity of metazoan proteomes. After definition of the exons, the spliceosome is activated by a series of sequential structural rearrangements. Formation of the first ATP-independent spliceosomal complex commits the pre-mRNA to the general splicing pathway. However, the time at which a commitment to a specific splice site choice and pairing is made is unknown. Here, we demonstrate that alternative splicing patterns are irreversibly chosen at a kinetic step different from the ATP-independent commitment to splicing. Splice sites become committed at the first ATP-dependent spliceosomal complex when rearrangements lock U2 snRNP onto the pre-mRNA. Thus, commitment to the splicing pathway and commitment to splice site pairing are separate steps during spliceosomal assembly, and ATP hydrolysis drives the irreversible juxtaposition of exons within the spliceosome.
Department of Microbiology and Molecular Genetics, College of Medicine, University of California, Irvine, Irvine, CA 92697, USA.
Sharlene R
SR
Lim
Klemens J
KJ
Hertel
D000818:Animals; D006801:Humans; D007700:Kinetics; D012326:RNA Splicing / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis*; D017381:Spliceosomes / Q000235:genetics / Q000502:physiology*
D012333:RNA, Messenger