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Role for the Ssu72 C-terminal domain phosphatase in RNA polymerase II transcription elongation.

The RNA polymerase II (RNAP II) transcription cycle is accompanied by changes in the phosphorylation status of the C-terminal domain (CTD), a reiterated heptapeptide sequence (Y(1)S(2)P(3)T(4)S(5)P(6)S(7)) present at the C terminus of the largest RNAP II subunit. One of the enzymes involved in this process is Ssu72, a CTD phosphatase with specificity for serine-5-P. Here we report that the ssu72-2-encoded Ssu72-R129A protein is catalytically impaired in vitro and that the ssu72-2 mutant accumulates the serine-5-P form of RNAP II in vivo. An in vitro transcription system derived from the ssu72-2 mutant exhibits impaired elongation efficiency. Mutations in RPB1 and RPB2, the genes encoding the two largest subunits of RNAP II, were identified as suppressors of ssu72-2. The rpb1-1001 suppressor encodes an R1281A replacement, whereas rpb2-1001 encodes an R983G replacement. This information led us to identify the previously defined rpb2-4 and rpb2-10 alleles, which encode catalytically slow forms of RNAP II, as additional suppressors of ssu72-2. Furthermore, deletion of SPT4, which encodes a subunit of the Spt4-Spt5 early elongation complex, also suppresses ssu72-2, whereas the spt5-242 allele is suppressed by rpb2-1001. These results define Ssu72 as a transcription elongation factor. We propose a model in which Ssu72 catalyzes serine-5-P dephosphorylation subsequent to addition of the 7-methylguanosine cap on pre-mRNA in a manner that facilitates the RNAP II transition into the elongation stage of the transcription cycle.

Pubmed ID: 17101794


  • Reyes-Reyes M
  • Hampsey M


Molecular and cellular biology

Publication Data

February 19, 2007

Associated Grants

  • Agency: NIGMS NIH HHS, Id: GM 008360
  • Agency: NIGMS NIH HHS, Id: GM 55145
  • Agency: NIGMS NIH HHS, Id: GM 58389
  • Agency: NIGMS NIH HHS, Id: R01 GM 39484
  • Agency: NIGMS NIH HHS, Id: R01 GM 68887

Mesh Terms

  • Alanine
  • Alleles
  • Amino Acid Sequence
  • Arginine
  • Carrier Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA, Fungal
  • Models, Genetic
  • Molecular Sequence Data
  • Nuclear Proteins
  • Phenotype
  • Phosphoprotein Phosphatases
  • Protein Binding
  • Protein Structure, Secondary
  • RNA Polymerase II
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Sequence Analysis, DNA
  • Suppression, Genetic
  • TATA-Binding Protein Associated Factors
  • Transcription Factor TFIID
  • Transcription, Genetic
  • Transcriptional Elongation Factors
  • mRNA Cleavage and Polyadenylation Factors