On how a transcription factor can avoid its proteolytic activation in the absence of signal transduction

Abstract

pH by the products of the six pal genes (Denison et al., Universidad del País Vasco, Apdo. 1072, San Sebastián 20080, Spain, 1995, 1998 Maccheroni et al., 1997 form containing the~248-250 N-terminal residues Mingot et al., 1999), which activates expres- 5 Corresponding author e-mail: penalva@cib.csic.es sion of genes expressed preferentially under alkaline growth conditions (Espeso et al., 1993;Tilburn et al., In response to alkaline ambient pH, the Aspergillus 1995; Espeso and Peñalva, 1996) and represses genes nidulans PacC transcription factor mediating pH reguexpressed preferentially at acidic pH (Tilburn et al., lation of gene expression is activated by proteolytic 1995; Hutchings et al., 1999; E.A.Espeso and H.N.Arst, removal of a negative-acting C-terminal domain. We submitted). The PacC DNA binding domain (DBD), demonstrate interactions involving the~150 C-terminal containing three Cys 2 His 2 zinc fingers and binding to PacC residues and two regions located immediately GCCARG promoter sites ; Espeso downstream of the DNA binding domain. Our data et al., 1997), is located centrally within the processed form. indicate two full-length PacC conformations whoseThe alkaline pH-sensitive step in the regulatory cascade relative amounts depend upon ambient pH: one 'open' appears to be the accessibility of the PacC primary and accessible for processing, the other 'closed' and translation product to the processing protease, suggesting inaccessible. The location of essential determinants for that PacC alternates between protease-resistant and proteolytic processing within the two more upstream protease-sensitive conformations in response to ambient interacting regions probably explains why the interpH (Mingot et al., 1999). Loss-of-function pal -mutations actions prevent processing, whereas the direct preventing ambient pH signal transduction and PacC involvement of the C-terminal region in processingproteolytic processing (Caddick et al., 1986; Denison preventing interactions explains why C-terminal trun Tilburn et al., 1995;Negrete-Urtasun et al., cating mutations result in alkalinity mimicry and pH-1999) lead to an acidity-mimicking phenotype, as do null independent processing. A mutant PacC deficient in (pacC -) or partial loss-of-function (pacC ϩ/-) mutations in pH signal response and consequent processing behaves pacC. Gain-of-function pacC c mutations have an alkalinas though locked in the 'closed' form. Single-residue ity-mimicking phenotype, obviating the need for ambient substitutions, obtained as mutations bypassing the need pH signalling and resulting in constitutive (i.e. pH-indefor pH signal transduction, identify crucial residues in pendent) PacC processing (Caddick et al., 1986; Orejas each of the three interactive regions and overcome Tilburn et al., 1995;Mingot et al., 1999). processing deficiency in the 'permanently closed ' Most extant pacC c mutations result in truncation of 100-mutant.412 residues from the C-terminus of PacC, suggesting a Keywords: Aspergillus nidulans/PacC/pH regulation...

Dominant Active Alleles of RIM101(PRR2) Bypass the pH Restriction on Filamentation of Candida albicans

“…PacC is synthesized as a 687-residue inactive precursor, which is activated when cells are cultured at an alkaline pH. Activation occurs by proteolysis around residues 252 to 254, approximately 90 amino acids carboxy-terminal to the zinc finger domain (9,25). The carboxy terminus is essential to the pH dependence of activation and appears to control accessibility of the proteolytic site (9,25).…”

“…Activation occurs by proteolysis around residues 252 to 254, approximately 90 amino acids carboxy-terminal to the zinc finger domain (9,25). The carboxy terminus is essential to the pH dependence of activation and appears to control accessibility of the proteolytic site (9,25). Thus, mutations that cause premature termination and loss of the carboxy terminus result in proteolytic activation irrespective of ambient pH (9,25).…”

“…The carboxy terminus is essential to the pH dependence of activation and appears to control accessibility of the proteolytic site (9,25). Thus, mutations that cause premature termination and loss of the carboxy terminus result in proteolytic activation irrespective of ambient pH (9,25). Since PacC is required for transcriptional activation of alkaline-expressed genes and repression of acid-expressed genes, these truncating mutations can result in constitutive expression of alkaline-expressed genes and constitutive repression of acid-expressed genes (39).…”

Relationship between Secondary Metabolism and Fungal Development

“…At acidic pHs, the PacC protein is in an inactive conformation and is unable to bind target sites. At alkaline pHs, the PacC protein is cleaved (40), producing an active form. This activated PacC isoform can then bind to the promoters of target genes, activating the expression of alkaline expressed genes, and repressing the expression of acid expressed genes.…”

Regulation of Gene Expression by Ambient pH in Filamentous Fungi and Yeasts

“…2A). A number of regions are rich in certain amino acids (95), but the significance of this is unclear with the possible exception of a glycine-plus-prolinerich region beginning at residue 314 (see below) (41,122). An eye-catching feature is the presence of three perfect copies and one imperfect copy of a 6-residue direct repeat in which the perfect copies contain only acidic and glutamine residues (122).…”