title: On how a transcription factor can avoid its proteolytic activation in the absence of signal transduction.
abstract: In response to alkaline ambient pH, the Aspergillus nidulans PacC transcription factor mediating pH regulation of gene expression is activated by proteolytic removal of a negative-acting C-terminal domain. We demonstrate interactions involving the approximately 150 C-terminal PacC residues and two regions located immediately downstream of the DNA binding domain. Our data indicate two full-length PacC conformations whose relative amounts depend upon ambient pH: one 'open' and accessible for processing, the other 'closed' and inaccessible. The location of essential determinants for proteolytic processing within the two more upstream interacting regions probably explains why the interactions prevent processing, whereas the direct involvement of the C-terminal region in processing-preventing interactions explains why C-terminal truncating mutations result in alkalinity mimicry and pH-independent processing. A mutant PacC deficient in pH signal response and consequent processing behaves as though locked in the 'closed' form. Single-residue substitutions, obtained as mutations bypassing the need for pH signal transduction, identify crucial residues in each of the three interactive regions and overcome the processing deficiency in the 'permanently closed' mutant.
authors.affiliation: Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas del CSIC, Velázquez 144, Madrid 28006, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Espeso
authors.forename: T
authors.initials: T
authors.lastname: Roncal
authors.forename: E
authors.initials: E
authors.lastname: Díez
authors.forename: L
authors.initials: L
authors.lastname: Rainbow
authors.forename: E
authors.initials: E
authors.lastname: Bignell
authors.forename: J
authors.initials: J
authors.lastname: Alvaro
authors.forename: T
authors.initials: T
authors.lastname: Suárez
authors.forename: S H
authors.initials: SH
authors.lastname: Denison
authors.forename: J
authors.initials: J
authors.lastname: Tilburn
authors.forename: H N
authors.initials: HN
authors.lastname: Arst
authors.forename: M A
authors.initials: MA
authors.lastname: Peñalva
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D010450:Endopeptidases / Q000378:metabolism; D005656:Fungal Proteins; D005786:Gene Expression Regulation; D005800:Genes, Fungal; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D008969:Molecular Sequence Data; D017354:Point Mutation; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015398:Signal Transduction; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D016335:Zinc Fingers / Q000235:genetics
chemical_list: D005656:Fungal Proteins; C092394:PacC protein, Aspergillus; D014157:Transcription Factors; D010450:Endopeptidases