Role of the essential yeast protein PSU1 in p6anscriptional enhancement by the ligand-dependent activation function AF-2 of nuclear receptors.
Nuclear receptors (NRs) can function as ligandinducible transregulators in both mammalian and yeast cells, indicating that important features of transcriptional control have been conserved throughout evolution. We report here the isolation and characterization of an essential yeast protein of unknown function, PSU1, which exhibits properties expected for a co-activator/mediator of the ligand-dependent activation function AF-2 present in the ligand-binding domain (LBD, region E) of NRs. PSU1 interacts in a ligand-dependent manner with the LBD of several NRs, including retinoic acid (RARalpha), retinoid X (RXRalpha), thyroid hormone (TRalpha), vitamin D3 (VDR) and oestrogen (ERalpha) receptors. Importantly, both in yeast and in vitro, these interactions require the integrity of the AF-2 activating domain. When tethered to a heterologous DNA-binding domain, PSU1 can activate transcription on its own. By using yeast reporter cells that express PSU1 conditionally, we show that PSU1 is required for transactivation by the AF-2 of ERalpha. Taken together these data suggest that in yeast, PSU1 is involved in ligand-dependent transactivation by NRs. Sequence analysis revealed that in addition to a highly conserved motif found in a family of MutT-related proteins, PSU1 contains several alpha-helical leucine-rich motifs sharing the consensus sequence LLxPhiL (x, any amino acid; Phi, hydrophobic amino acid) in regions that elicit either transactivation or NR-binding activity.
Gaudon
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Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Collège de France, BP 163, 67404 Illkirch Cedex, France.
Chambon
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Losson
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D000595:Amino Acid Sequence; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000737:chemistry / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*
D005656:Fungal Proteins; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D029702:Schizosaccharomyces pombe Proteins; C119250:Sui1 protein, S pombe; D015534:Trans-Activators; D014157:Transcription Factors