Cytoplasmic poly(A) polymerases mediate cellular responses to S phase arrest.
The S-M checkpoint delays mitosis until DNA replication is complete; cells defective in this checkpoint lose viability when DNA replication is inhibited. This inviability can be suppressed in fission yeast by overexpression of Cid1 or the related protein Cid13. Fission yeast contain six cid1/cid13-like genes, whereas budding yeast has just two, TRF4 and TRF5. Trf4 and Trf5 were recently reported to comprise an essential DNA polymerase activity required for the establishment of sister chromatid cohesion. In contrast, we find that Cid1 is not a DNA polymerase but instead uses RNA substrates and has poly(A) polymerase activity. Unlike the previously characterized yeast poly(A) polymerase, which is a nuclear enzyme, Cid1 and Cid13 are constitutively cytoplasmic. Cid1 has a degree of substrate specificity in vitro, consistent with the notion that it targets a subset of cytoplasmic mRNAs for polyadenylation in vivo, hence increasing their stability and/or efficiency of translation. Preferred Cid1 targets presumably include mRNAs encoding components of the S-M checkpoint, whereas Cid13 targets are likely to be involved in dNTP metabolism. Cytoplasmic polyadenylation is known to be an important regulatory mechanism during early development in animals. Our findings in yeast suggest that this level of gene regulation is of more general significance in eukaryotic cells.
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Rebecca L
RL
Cancer Research UK Molecular Oncology Laboratory, University of Oxford Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
Martinho
Rui G
RG
Wang
Shao-Win
SW
Carr
Antony M
AM
Norbury
Chris J
CJ
D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D064447:Checkpoint Kinase 2; D003593:Cytoplasm / Q000201:enzymology; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D006918:Hydroxyurea / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D011062:Polynucleotide Adenylyltransferase / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase / Q000187:drug effects / Q000502:physiology*; D012568:Schizosaccharomyces / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D011994:Recombinant Proteins; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C456840:rad3 protein, S pombe; C459739:Cid13 protein, S pombe; D011062:Polynucleotide Adenylyltransferase; D010749:Phosphoprotein Phosphatases; D006918:Hydroxyurea