Nuclear mRNA surveillance in THO/sub2 mutants is triggered by inefficient polyadenylation.
The yeast THO complex and the associated RNA helicase Sub2p are important mRNP maturation factors. Transcripts produced in THO/sub2 mutants are subject to degradation by a surveillance mechanism that involves the nuclear RNA exosome. Here we show that inefficient polyadenylation forms the basis of this accelerated mRNA decay. A genetic screen reveals extensive interactions between deletions of THO subunits and mRNA 3' end processing mutants. Nuclear run-ons strengthen this link by showing premature transcription termination close to polyadenylation sites in THO/sub2 mutants in vivo. Moreover, in vitro, pre-mRNA substrates are poorly polyadenylated and consequently unstable in extracts from THO/sub2 mutant strains. Decreased polyadenylation correlates with a specific downregulation of the poly(A)-polymerase cofactor Fip1p by the ubiquitin/proteasome pathway. Both polyadenylation defects and Fip1p instability depend on the nuclear exosome component Rrp6p and its activator Trf4p. We suggest that removal of aberrant mRNA is facilitated by direct regulation of polyadenylation activity.
Saguez
Cyril
C
Centre for mRNP Biogenesis and Metabolism, Aarhus University, C.F. Møllers Alle, Building 130, DK-8000 Aarhus C, Denmark.
Schmid
Manfred
M
Olesen
Jens Raabjerg
JR
Ghazy
Mohamed Abd El-Hady
MA
Qu
Xiangping
X
Poulsen
Mathias Bach
MB
Nasser
Tommy
T
Moore
Claire
C
Jensen
Torben Heick
TH
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D026905:Amino Acid Transport Systems / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D018389:Codon, Nonsense; D015536:Down-Regulation; D046912:Multiprotein Complexes / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D011061:Poly A / Q000378:metabolism; D026723:Polyadenylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism; D020871:RNA Stability; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000378:metabolism; D039221:mRNA Cleavage and Polyadenylation Factors / Q000378:metabolism
D026905:Amino Acid Transport Systems; C429560:BAP3 protein, S cerevisiae; D018389:Codon, Nonsense; C450579:FIP1 protein, S cerevisiae; D046912:Multiprotein Complexes; D012322:RNA Precursors; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D039221:mRNA Cleavage and Polyadenylation Factors; D011061:Poly A; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C027900:RNA-dependent ATPase