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spliceosome
Function:
- ribonucleoprotein complex that removes introns from transcribed pre-nRNA, i.e. facilitates RNA splicing
Structure:
- consists of U1, U2, U4, U5, U6 snRNPs
Notes:
Spliceosome assembly:
- U1 snRNP binds to 5' end splice site of hnRNA & recruits other factors to form the 'E complex'
- U2 snRNP is recruited to the branch region of a splice site through interactions with the 'E complex' & becomes tightly associated with the branch point sequence to form 'complex A'
- a duplex is formed between U2 snRNA & the hnRNA branch region bulging out & specifying the branch adenosine for trans- esterfication
- the presence of a pseudouridine residue in the U2 snRNA, nearly opposite the branch site, results in altered conformation of the RNA-RNA duplex upon U2 snRNP binding
- pseudouridine places the 2'OH of the bulged adenosine in a favorable position for the 1st step of splicing
- the U4/U5/U6 tri-snRNP is recruited to the assembling spliceosome to form 'complex B' & following several rearrangements, 'Complex C' (the splicesome) is activated for catalysis
Specific
spliceosome C complex
U12-type spliceosome (minor spliceosome)
General
endoribonuclease
ligase or synthetase
multienzyme complex
regulatory molecule
Properties
STATE: Inactive
MOTIF: active site
References
- Alberts et al Molecular Biology of the Cell,
2nd ed. 1989, pg 533
- Wikipedia: Spliceosome
http://en.wikipedia.org/wiki/spliceosome
Components
U1-snRNP; U1 small nuclear ribonucleoprotein
U2-snRNP; U2 small nuclear ribonucleoprotein
U4-snRNP; U4 small nuclear ribonucleoprotein
U5-snRNP; U5 small nuclear ribonucleoprotein
U6-snRNA