A Gal4-σ54 Hybrid Protein that Functions as a Potent Activator of RNA Polymerase II Transcription in Yeast

Bo Shiun Chen, Zu Wen Sun, Michael Hampsey

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The bacterial σ54 protein associates with core RNA polymerase to form a holoenzyme complex that renders cognate promoters enhancer-dependent. Although unusual in bacteria, enhancer-dependent transcription is the paradigm in eukaryotes. Here we report that a fragment of Escherichia coli σ54 encompassing amino acid residues 29-177 functions as a potent transcriptional activator in yeast when fused to a Gal4 DNA binding domain. Activation by Gal4-σ54 is TATA-dependent and requires the SAGA coactivator complex, suggesting that Gal4-σ 54 functions by a normal mechanism of transcriptional activation. Surprisingly, deletion of the AHC1 gene, which encodes a polypeptide unique to the ADA coactivator complex, stimulates Gal4-σ54 -mediated activation and enhances the toxicity of Gal4-σ54. Accordingly, the SAGA and ADA complexes, both of which include Gcn5 as their histone acetyltransferase subunit, exert opposite effects on transcriptional activation by Gal4-α54. Gal4-σ54 activation and toxicity are also dependent upon specific σ54 residues that are required for activator-responsive promoter melting by σ54 in bacteria, implying that activation is a consequence of σ 54-specific features rather than a structurally fortuitous polypeptide fragment. As such, Gal4-σ54 represents a novel tool with the potential to provide insight into the mechanism by which natural activators function in eukaryotic cells.

Original languageEnglish (US)
Pages (from-to)23881-23887
Number of pages7
JournalJournal of Biological Chemistry
Issue number26
StatePublished - Jun 29 2001

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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