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Function of the Ski4p (Csl4p) and Ski7p Proteins in 3’-to5’ Degradation of mRNA
Ambro van Hoof, Robin R. Staples, Richard E. Baker, and Roy Parker
Molcecular and Cellular Biology, p8230-8243 (2000)
Introduction
Yeast virus
Annu. Rev. Genet. 30:109-39 (1996)
Annu. Rev. Microbiol. 46:347-75 (1992)
Cryo-EM 16Å
Crystal structure 3.4Å
J. Mol. Recognit. 18:158-168 (2005)
The viral replication cycles of L-A and its satellites
J. Cell. Biol. 138:975-985 (1997 )
Annu. Rev. Genet. 30:109-39 (1996)
SKI antiviral system
J Bacteriol. 136(3): 1002–1007 (1978)
Trends. Microbiol. 1:294-298 (1993)
mRNA degradation in yeast
7mGppp
Decapping (Dcp1p, Dcp2p)
p
A60-80
mRNA
mRNA
A60-80
Deadenylation
7mGppp
3’-5’ degradation
5’-3’ degradation (Xrn1p)
mRNA
A60-80
mRNA
7mGppp
mRNA
The exosome: a conserved eukaryotic RNA processing complex containing
multiple 3’-5’ exoribonuclease activities. Cell, 91, 457-466 (1997)
Rrp4p,Rrp41/Ski6p, Rrp42p, Rrp43p, Rrp44p
A0-10
The 3’ to 5’ degradation of yeast mRNAs is a general mechanism for mRNA turnover
that requires the SKI2 DEVH box protein and 3’ to 5’ exonucleases of the exosome
complex EMBO J. 1497-1506 (1998)
The SKI2, SKI3, SKI6/RRP41, SKI8 and RRP4 gene products
are required for 3’ to 5’ decay of mRNA
The yeast antiviral proteins Ski2p, Ski3p, and Ski8p exist as a complex in vivo
RNA 6:449-457 (2000)
The ski4-1 and ski7Δ mutations affect the metabolism of a degradation
intermediate of MFA2pG mRNA
The ski4-1 and ski7Δ mutations stabilize a degradation intermediate of
MFA2pG mRNA
Strains containing either ski4-1 or ski7Δ in combination with dcp1-2 or dcp2-7
are not able to grow under conditions restrictive for the decapping defect
SKi4p and Ski7p proteins are required for 3’-5’ mRNA degradation as are the
components of the exosome and the Ski2p,SKi3p, and Ski8p protein.
The ski4-1 mutation is complemented by a wild-type (WT) CSl4 gene
A mutation in the conserved S1 RNA binding domain of Csl4p is
responsible for the ski4-1 phenotype
Two mutations of Ski4p : R65K, G253E
The SKI4 gene is identical to the CSl4 gene
The ski4-1 mutation does not affect all Csl4p functions
ski6
The csl4-1 mutation affects rRNA processing but not mRNA degradation
rRNA processing
mRNA degradation
The ski4-1 allele genetically separates the functions of
the exosome in rRNA processing and mRNA decay
The ski7Δ and hgs1Δ mutations do not affect 5.8S rRNA or U4 snRNA
processing or 5’ ETS degradation
The SKI7 gene is specifically required for mRNA degradation by the exosome
Summary
1. The Ski4p and Ski7p proteins are required for mRNA
degradation.
2. The SKI4 gene is identical to the CSL4 gene
3. The ski4-1 allele genetically separates the functions of
the exosome in rRNA processing and mRNA decay
4.The SKI7 gene is specifically required for mRNA
degradation by the exosome.
SKI 1: Xrn1p enzyme (5’ to 3’ exoribonuclease)
SKI 2: 1287 a.a. putative RNA helicase
SKI 3: 1432 a.a. tetratricopeptide repeat (TRP) protein
SKI 4: 195 a.a. S1 domain (Csl4p)
SKI 6: 264 a.a. Rrp41p (3’-5’ exoribonuclease)
SKI 7: 747 a.a. GTPase domain ( translation elongation factor EF1A/
translation termination factor eRF3)
SKI 8: 397 a.a. five WD-40 (beta-transducin) repeats protein
Componenets of the exosome complex