Distinct regions of Cu(I).ACE1 contact two spatially resolved DNA major groove sites

Gelatin expression from an engineered Saccharomyces cerevisiae CUP1 promoter in Pichia pastoris

The methylotrophic yeast Pichia pastoris (reclassified as Komagataella phaffii) is a versatile protein expression system, yet many commonly used promoters have attributes undesirable for fermentation or its optimization. Hence, the copper-inducible CUP1 gene promoter from the related yeast Saccharomyces cerevisiae was used to express human gelatin. Multimerization of a potential copper response element in the CUP1 promoter, a S. cerevisiae Ace1p binding site, significantly increased gelatin expression. Expression was induced by copper in a dose-dependent fashion and was not dependent on cell density. Gelatin was additionally induced in standard copper-containing fermentation basal salts media. Removal of a S. cerevisiae heat shock factor (Hsf1p) binding site reduced copper-dependent gelatin induction suggesting that a similar protein may regulate this promoter in P. pastoris. This engineered copper inducible promoter expands the yeast recombinant protein production tool kit.

Activation of Haa1 and War1 transcription factors by differential binding of weak acid anions in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, Haa1 and War1 transcription factors are involved in cellular adaptation against hydrophilic weak acids and lipophilic weak acids, respectively. However, it is unclear how these transcription factors are differentially activated depending on the identity of the weak acid. Using a field-effect transistor (FET)-type biosensor based on carbon nanofibers, in the present study we demonstrate that Haa1 and War1 directly bind to various weak acid anions with different affinities. Haa1 is most sensitive to acetate, followed by lactate, whereas War1 is most sensitive to benzoate, followed by sorbate, reflecting their differential activation during weak acid stresses. We show that DNA binding by Haa1 is induced in the presence of acetic acid and that the N-terminal Zn-binding domain is essential for this activity. Acetate binds to the N-terminal 150-residue region, and the transcriptional activation domain is located between amino acid residues 230 and 483. Our data suggest that acetate binding converts an inactive Haa1 to the active form, which is capable of DNA binding and transcriptional activation.

Transcriptional Regulation of Gene Expression by Metalloproteins

FNR and SoxR are transcriptional regulators containing an iron–sulfur cluster. The iron–sulfur cluster in FNR acts as an oxygen sensor by reacting with oxygen. The structural change of the iron–sulfur cluster takes place when FNR senses oxygen, which regulates the transcriptional regulator activity of FNR through the change of the quaternary structure. SoxR contains the [2Fe–2S] cluster that regulates the transcriptional activator activity of SoxR. Only the oxidized SoxR containing the [2Fe–2S]2+ cluster is active as the transcriptional activator. CooA is a transcriptional activator containing a protoheme that acts as a CO sensor. CO is a physiological effector of CooA and regulates the transcriptional activator activity of CooA. In this review, the biochemical and biophysical properties of FNR, SoxR, and CooA are described.

Copper Acquisition and Utilization in Fungi

Fungal cells colonize and proliferate in distinct niches, from soil and plants to diverse tissues in human hosts. Consequently, fungi are challenged with the goal of obtaining nutrients while simultaneously elaborating robust regulatory mechanisms to cope with a range of availability of nutrients, from scarcity to excess. Copper is essential for life but also potentially toxic. In this review we describe the sophisticated homeostatic mechanisms by which fungi acquire, utilize, and control this biochemically versatile trace element. Fungal pathogens, which can occupy distinct host tissues that have their own intrinsic requirements for copper homeostasis, have evolved mechanisms to acquire copper to successfully colonize the host, disseminate to other tissues, and combat host copper bombardment mechanisms that would otherwise mitigate virulence.

Transmission line model analysis of transcription factors binding to oligoduplexes - differentiation of the effect of single nucleotide modifications

Advanced impedance spectroscopy analysis based on the transmission line model (TLM) is explored as a novel QCM acoustic biosensing platform for the detection of the single point mutation effect on the binding of the transcription factors (TFs) to immobilized DNA oligoduplexes and the characterization of the protein-DNA mechanical properties.

Genetically encoded copper(I) reporters with improved response for use in imaging

Copper represents one of the most important biological metal ions due to its role as a catalytic cofactor in a multitude of proteins. However, an excess of copper is highly toxic. Thus, copper is heavily regulated, and copper homeostasis is controlled by many metalloregulatory proteins in various organisms. Here we report a genetically encoded copper(I) probe capable of monitoring copper fluctuations inside living cells. We insert the copper regulatory protein Ace1 into a yellow fluorescent protein, which selectively binds copper(I) and generates improved copper(I) probes.

Identification of a DNA-binding site for the transcription factor Haa1, required for Saccharomyces cerevisiae response to acetic acid stress

The transcription factor Haa1 is the main player in reprogramming yeast genomic expression in response to acetic acid stress. Mapping of the promoter region of one of the Haa1-activated genes, TPO3, allowed the identification of an acetic acid responsive element (ACRE) to which Haa1 binds in vivo. The in silico analysis of the promoter regions of the genes of the Haa1-regulon led to the identification of an Haa1-responsive element (HRE) 5'-GNN(G/C)(A/C)(A/G)G(A/G/C)G-3'. Using surface plasmon resonance experiments and electrophoretic mobility shift assays it is demonstrated that Haa1 interacts with high affinity (K(D) of 2 nM) with the HRE motif present in the ACRE region of TPO3 promoter. No significant interaction was found between Haa1 and HRE motifs having adenine nucleotides at positions 6 and 8 (K(D) of 396 and 6780 nM, respectively) suggesting that Haa1p does not recognize these motifs in vivo. A lower affinity of Haa1 toward HRE motifs having mutations in the guanine nucleotides at position 7 and 9 (K(D) of 21 and 119 nM, respectively) was also observed. Altogether, the results obtained indicate that the minimal functional binding site of Haa1 is 5'-(G/C)(A/C)GG(G/C)G-3'. The Haa1-dependent transcriptional regulatory network active in yeast response to acetic acid stress is proposed.

A catalogue of eukaryotic transcription factor types, their evolutionary origin, and species distribution

Transcription factors (TFs) play key roles in the regulation of gene expression by binding in a sequence-specific manner to genomic DNA. In eukaryotes, DNA binding is achieved by a wide range of structural forms and motifs. TFs are typically classified by their DNA-binding domain (DBD) type. In this chapter, we catalogue and survey 91 different TF DBD types in metazoa, plants, fungi, and protists. We briefly discuss well-characterized TF families representing the major DBD superclasses. We also examine the species distributions and inferred evolutionary histories of the various families, and the potential roles played by TF family expansion and dimerization.

Copper homeostasis in Enterococcus hirae

Copper is an essential component of life because of its convenient redox potential of 200-800 mV when bound to protein. Extensive insight into copper homeostasis has only emerged in the last decade and Enterococcus hirae has served as a paradigm for many aspects of the process. The cop operon of E. hirae regulates copper uptake, availability, and export. It consists of four genes that encode a repressor, CopY, a copper chaperone, CopZ, and two CPx-type copper ATPases, CopA and CopB. Most of these components have been conserved across the three evolutionary kingdoms. The four Cop proteins have been studied in vivo as well as in vitro and their function is understood in some detail.

Haa1, a protein homologous to the copper-regulated transcription factor Ace1, is a novel transcriptional activator

The Saccharomyces cerevisiae genome contains a predicted gene, YPR008w, homologous to the gene encoding the copper-activated transcription factor Ace1. The product of the YPR008w gene, designated Haa1, regulates the transcription of a set of yeast genes, many of which encode membrane proteins. Two main target genes of Haa1 are the multidrug resistance gene YGR138c and the YRO2 homolog to the plasma membrane Hsp30. Haa1 is localized to the nucleus. Haa1-induced expression of YGR138c and YRO2 appears to be direct. Induction of HAA1 using a GAL1/HAA1 fusion gene resulted in rapid galactose-induced expression of both HAA1 and target genes. Although Haa1 has a sequence very similar to the Cu-activated DNA binding domain of Ace1, expression of Haa1 target genes was found to be independent of the copper status of cells. Haa1 does not exhibit metalloregulation in cells incubated with a range of transition metal salts. Haa1 does not exhibit any cross-talk with Ace1. Overexpression of Haa1 does not compensate for cells lacking a functional Ace1. The lack of metalloregulation of Haa1 despite the strong sequence similarity to the copper regulatory domain of Ace1 is discussed.

Changes in DNA conformation induced by gamma irradiation in the presence of copper

Gamma irradiation of DNA solutions containing copper causes changes in DNA conformation in oligonucleotides and in natural and synthetic DNAs. Diagnostic for these conformational changes is a ubiquitous 187-nm peak in the circular dichroism (CD) difference spectrum that has been predicted for a transformation from a right-handed to a left-handed helical DNA conformation. Changes in CD are correlated with changes in the UV spectrum. Reduction of DNA-bound Cu(II) to Cu(I) with ascorbic acid produces similar changes in CD spectra. These changes can be produced by the peroxy radical anion (O2*-) and the OH radical in the presence of copper. O2*- is approximately twice as efficient as *OH in initiating these changes in natural DNA. The changes in DNA conformation induced by ionizing radiation are remarkable in that they are dependent on the copper-ion concentration in a highly nonlinear manner at low copper concentrations and are not observed in the absence of copper ions. Possible implications of our results for radiobiological and oxidative damage in the cell nucleus are discussed.

Septamer element-binding proteins in neuronal and glial differentiation

Differentiation of progenitors into neurons and glia is regulated by interactions between regulatory DNA elements of neuron- and glia-specific genes and transcription factors that are differentially expressed by progenitors at progressive stages of neural development. We have identified a novel DNA regulatory element (TTTGCAT = septamer) present on the enkephalin (ENK), neuronal cell adhesion molecule, neurofilament of 68 kDa (NF68), growth-associated protein of 43 kDa, glial high-affinity glutamine transporter, tyrosine hydroxylase, etc., genes. When septamer function was blocked by introducing septamer competitor DNA into primary differentiating neural cultures, mRNA levels of ENK, NF68, and glial fibrillary acidic protein decreased by 50-80%, whereas no effect was seen using a control DNA. Septamer elements serve as binding sites for lineage-specific multimeric complexes assembled from three distinct nuclear proteins. Progenitors express a 16 kDa protein (p-sept) which binds to DNA as a homodimer (detected as the 32 kDa P-band). Cells that entered the neuronal lineage express an additional 29 kDa protein (n-sept) that binds to the homodimerized p-sept, and together they form a 62 kDa multimer (detected as N-band). Cells that entered the glial lineage express a distinct 23 kDa protein (g-sept), which along with the homodimerized p-sept form a 56 kDa multimer (observed as G-band). The binding of the distinct protein complexes (P, G, and N) to the septamer site causes a lineage-specific DNA bending (P = 53 degrees; G = 72 degrees; and N = 90 degrees ), which may contribute to the regulatory effect of the septamer interaction. In summary, septamer and its binding proteins represent novel protein-DNA interactions that may contribute to the regulation of neuroglial differentiation in the developing mammalian CNS.

Structure-function analysis of the protein-binding domains of Mac1p, a copper-dependent transcriptional activator of copper uptake in Saccharomyces cerevisiae

The Mac1 protein in Saccharomyces cerevisiae is essential for the expression of yeast high affinity copper uptake. A positive transcription factor, Mac1p binds via its N-terminal domain to GCTC elements in the promoters of CTR1 and FRE1, encoding a copper permease and metal reductase, respectively. Mac1p-dependent transcriptional activation is negatively regulated by copper. We have mapped the domains in Mac1p responsible for its nuclear localization and for the protein-protein interactions that underlie its transcriptional activity. Immunofluorescence studies indicate that Mac1p contains two nuclear localization signals, one each in the N- and C-terminal halves of the protein. Yeast one-hybrid analysis demonstrates that the copper-dependent transcriptional activity in Mac1p resides primarily in a cysteine-rich element encompassing residues 264-279. Two-hybrid analysis indicates that a copper-independent Mac1p-Mac1p interaction linked to DNA binding is due primarily to a predicted helix in the C-terminal region of the protein encompassing residues 388-406. Point mutations within this putative helix abrogate the Mac1-Mac1 interaction in vivo and formation of a ternary (Mac1p)(2).DNA complex in vitro. When produced in normal abundance, Mac1pI396D and Mac1pF400D helix mutants do not support transcriptional activation in vivo consistent with an essential Mac1p dimerization in transcriptional activation. Lastly, the one- and two-hybrid data indicate that an intramolecular interaction between the DNA-binding and transactivation domains negatively modulates Mac1p activity.

The Enterococcus hirae copper chaperone CopZ delivers copper(I) to the CopY repressor

Expression of the cop operon which effects copper homeostasis in Enterococcus hirae is controlled by the copper responsive repressor CopY. Purified Zn(II)CopY binds to a synthetic cop promoter fragment in vitro. Here we show that the 8 kDa protein CopZ acts as a copper chaperone by specifically delivering copper(I) to Zn(II)CopY and releasing CopY from the DNA. As shown by gel filtration and luminescence spectroscopy, two copper(I) are thereby quantitatively transferred from Cu(I)CopZ to Zn(II)CopY, with displacement of the zinc(II) and transfer of copper from a non-luminescent, exposed, binding site in CopZ to a luminescent, solvent shielded, binding site in CopY.

Evidence for (Mac1p)2.DNA ternary complex formation in Mac1p-dependent transactivation at the CTR1 promoter

The Mac1 protein in Saccharomyces cerevisiae is required for the expression CTR1 and FRE1, which, respectively, encode the copper permease and metal reductase that participate in copper uptake. Mac1p binds to a core GCTC sequence present as a repeated unit in the promoters of both genes. We show here that Mac1p DNA binding required an intact N-terminal protein domain that includes a likely zinc finger motif. This binding was enhanced by the presence of a TATTT sequence immediately 5' to the core GCTC, in contrast to a TTTTT one. This increased binding was demonstrated clearly in vitro in electrophoretic mobility shift assays that showed Mac1p.DNA complex formation to a single TATTTGCTC element but not to a TTTTTGCTC one. Furthermore, the fraction of Mac1p in a ternary (Mac1p)2.DNA complex in comparison to a binary Mac1p.DNA complex increased when the DNA included two TATTTGCTC elements. A similar increase in ternary complex formation was demonstrated upon homologous mutation of the FRE1 Mac1p-dependent promoter element. The in vivo importance of this ternary complex formation at the CTR1 promoter was indicated by the stronger trans-activity of this promoter mutated to contain two TATTT elements and the attenuated activity of a mutant promoter containing two TTTTT elements that in vitro supported only a weak ternary complex signal in the shift assay. The stronger binding to TATTT appeared due to a more favorable protein contact with adenine in comparison to thymine at this position. An in vivo two-hybrid analysis demonstrated a Mac1p-Mac1p protein-protein interaction. This Mac1p-Mac1p interaction may promote (Mac1p)2.DNA ternary complex formation at Mac1p-responsive upstream activating sequences.

Mapping of the DNA binding domain of the copper-responsive transcription factor Mac1 from Saccharomyces cerevisiae

Mac1 from Saccharomyces cerevisiae activates transcription of genes, including CTR1 in copper-deficient cells. N-terminal fusions of Mac1 with the herpes simplex VP16 activation domain were used to show that residues 1-159 in Mac1 constitute the minimal DNA binding domain. Mac1-(1-159) purified from Escherichia coli contains two bound Zn(II) ions. Electrophoretic mobility shift assays showed direct and specific binding by Mac1-(1-159) to a DNA duplex containing the copper-responsive element TTTGCTCA. The DNA binding affinity of Mac1-(1-159) for a duplex containing a single promoter element or an inverted repeat was 5 nM for the 1:1 complex. The N-terminal 40-residue segment of Mac1 is homologous to the DNA binding zinc module found in the copper-activated transcription factors Ace1 and Amt1. A MAC1 mutation yielding a Cys11 --> Tyr substitution at the first candidate zinc ligand position relative to Ace1 resulted in a loss of in vivo function. Two TTTGCTCA promoter elements are necessary for efficient Mac1-mediated transcriptional activation. The elements appear to function synergistically. Increasing the number of elements yields more than additive enhancements in CTR1 expression.

High-level production of human parathyroid hormone (hPTH) by induced expression in Saccharomyces cerevisiae

Saccharomyces cerevisiae was used as host for high-level production of intact human parathyroid hormone (hPTH). The yield increased about 30-fold by changing from the constitutive MFalpha promoter to the inducible CUP1 promoter in the expression cassettes, use of another host strain, and optimization of growth conditions where especially the pH value was crucial. The secreted products consisted mainly of intact hormone, hPTH(1-84). In addition, two C-terminally truncated forms that lacked the four or five last amino acid residues, hPTH(1-80) and hPTH(1-79), were identified. These hPTH forms migrated aberrantly by SDS-PAGE as 14-kDa proteins, while the real masses measured by mass spectrometry on HPLC-purified products were about 9 kDa. Availability of such easily purified truncated forms will be valuable for studies of how the C-terminal residues affect the structure and function of the hormone. Combination of mutations and disruptions of the host genes encoding proteinase A, B, carboxypeptidase Y, and Kex1p or Mkc7p did not influence the C-terminal deletions. The secretion of hPTH could be enhanced by overexpression of the yeast syntaxin gene SSO2, but the total level of the hormone was not improved due to impaired growth.

Solution structure of a zinc domain conserved in yeast copper-regulated transcription factors

The three dimensional structure of the N-terminal domain (residues 1-42) of the copper-responsive transcription factor Amtl from Candida glabrata has been determined by two-dimensional 1H-correlated nuclear magnetic resonance (NMR) methods. The domain contains an array of zinc-binding residues (Cys-X2-Cys-X8-Cys-X-His) that is conserved among a family of Cu-responsive transcription factors. The structure is unlike those of previously characterized zinc finger motifs, and consists of a three-stranded antiparallel beta-sheet with two short helical segments that project from one end of the beta-sheet. Conserved residues at positions 16, 18 and 19 form a basic patch that may be important for DNA binding.

Copper-regulatory domain involved in gene expression

Copper ion homeostasis in yeast is maintained through regulated expression of genes involved in copper ion uptake, Cu(I) sequestration, and defense against reactive oxygen intermediates. Positive and negative copper ion regulation is observed, and both effects are mediated by Cu(I)-sensing transcription factors. The mechanism of Cu(I) regulation is distinct for transcriptional activation versus transcriptional repression. Cu(I) activation of gene expression in S. cerevisiae and C. glabrata occurs through Cu-regulated DNA binding. The activation process involves Cu(I) cluster formation within the regulatory domain in Ace1 and Amt1. Cu(I) binding stabilizes a specific conformation capable of high-affinity interaction with specific DNA promoter sequences. Cu(I)-activated transcription factors are modular proteins in which the DNA-binding domain is distinct from the domain that mediates transcriptional activation. The all-or-nothing formation of the polycopper cluster permits a graded response of the cell to environmental copper. Cu(I) triggering may involve a metal exchange reaction converting Ace1 from a Zn(II)-specific conformer to a clustered Cu(I) conformer. The Cu(I) regulatory domain occurs in transcription factors from S. cerevisiae and C. glabrata. Sequence homologs are also known in Y. lipolytica and S. pombe, although no functional information is available for these candidate regulatory molecules. The presence of the Cu(I) regulatory domain in four distinct yeast strains suggests that this Cu-responsive domain may occur in other eukaryotes. Cu-mediated repression of gene expression in S. cerevisiae occurs through Cu(I) regulation of Mac1. Cu(I) binding to Mac1 appears to inhibit the transactivation domain. The Cu(I) specificity of this repression is likely to arise from formation of a polycopper thiolate cluster.

Copper-binding motifs in catalysis, transport, detoxification and signaling

Copper is required for many biological processes but is toxic at high cellular concentrations, so levels in the cell must be strictly controlled. Copper-binding motifs have been identified and characterized in many proteins. The way in which copper is coordinated by these motifs is important for the transport and distribution of intracellular copper and for the effective functioning of copper-dependent enzymes.

Copper-mediated repression of the activation domain in the yeast Mac1p transcription factor

The expression of a number of genes encoding products involved in copper ion uptake in yeast is specifically inhibited by copper ions. We show here that copper metalloregulation occurs through Cu-dependent repression of the transactivation activity of Mac1p. A segment of the yeast transcription factor Mac1p was identified that activated transcription in vivo in a heterologous system using fusion polypeptides with the yeast Gal4 DNA-binding domain. The Gal4/Mac1p hybrid exhibits transactivation activity that is repressed in cells cultured in the presence of copper salts and derepressed in cells with reduced copper uptake. The repressive effect is specific for copper ions. The concentration dependency of the Cu-inactivation of Gal4/Mac1p is similar to that of Cu-inhibition of CTR1 expression, a known Cu-regulated gene in vivo. Copper inhibition of gene expression is not observed with a Gal4/Mac1p chimera containing the MAC1(up1) substitution within the transactivation domain. Cells harboring the MAC1(up1) allele fail to attenuate FRE1 and CTR1 expression in a Cu-dependent manner. Additional MAC1(up) alleles exist within the first of two cysteine-rich sequence motifs adjacent to the His --> Gln MAC1(up1) encoded substitution. Thus, Cu-regulation of Mac1p function arises from a novel Cu-specific repression of the transactivation domain function. Models for the mechanism of Cu-repression of Mac1p function will be discussed.

Presence of a copper(I)-thiolate regulatory domain in the copper-activated transcription factor Amt1

The Amt1 transcription factor from Candida glabrata is activated by the formation of a tetracopper-thiolate cluster. Recombinant Amt1 (residues 1-110) is isolated as a Cu,ZnAmt1 complex. Previous mapping studies [Farrell et al. (1996) Biochemistry 35, 1571-1580] revealed that the Zn(II) site is enfolded by an independent, N-terminal domain consisting of residues 1-40. One prediction from the mapping study is that the tetracopper cluster is enfolded by residues 41-110. A truncated Amt1 peptide consisting of residues 37-110 was expressed and isolated as a CuAmt1 complex with 4 mol equiv of Cu(I) bound. The bound Cu(I) ions in the truncated Amt1 complex were spectroscopically similar to Cu(I) ions bound in the 110-mer Amt1 molecule in the energies and intensities of the ultraviolet S-->Cu charge transfer transitions and luminescence. Copper K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) of the truncated CuAmt1 complex revealed the same 2.26 A mean Cu-S bond distance as in the Cu,ZnAmt1 complex. A diagnostic feature of the polycopper-thiolate cluster in Cu,-ZnAmtl1 is the short 2.7 A Cu-Cu distance determined by Cu K-edge EXAFS. The truncated CuAmt1 complex had the same short 2.7 A Cu-Cu distance. The truncated CuAmt1 complex bound DNA specifically and with high affinity consistent with residues 41-110 being an independent domain stabilized by the tetracopper cluster. Thus, Amt1 consists of three independent and contiguous domains, an N-terminal Zn module (residues 1-40), an adjacent Cu regulatory domain (residues 41-110), and a C-terminal transcriptional activation domain. Cu(I) activation of Amt1 appears to consist of conversion of the 70-residue Cu regulatory domain from an inactive conformer to a structure containing the tetracopper cluster.

Identification of the Zn(II) site in the copper-responsive yeast transcription factor, AMT1: a conserved Zn module

The N-terminal metal-binding domains of the copper-activated yeast transcription factors, ACE1 and AMT1, bind to specific DNA sequences in a Cu-dependent fashion. Recombinant AMT1 and ACE1 metal-binding domains are isolated as Cu4Zn1-protein complexes. Site-directed mutagenesis of AMT1 was used in this study to map the ligands of the Cu(I) and Zn(II) ions. The results are consistent with the N-terminal halves of AMT1 and ACE1 consisting of two independent submodules, one binding a single Zn(II) ion and the second binding the tetracopper cluster. The basis of this conclusion is, first, that mutations of two cysteinyl codons and a histidyl codon in the first 42 residues of AMT1 do not alter DNA binding. In contrast, serine substitutions at four cysteine positions at codons 43, 61, 90, and 98 abolish DNA binding. We demonstrated previously that population of the Zn(II) site in AMT1 does not alter the ability of the protein to bind DNA but bound Cu(I) ions are essential for DNA binding [Thorvaldsen, J. L., et al. (1994) Biochemistry 33, 9566-9577]. Second, mutations in the N-terminal 42 residue segment reduce the Zn(II) content of purified mutant AMT1 molecules. Third, a synthetic peptide consisting of the N-terminal 42 residues in AMT1 forms a stable Zn(II) complex and substitution with Co(II) reveals an electronic spectrum identical to that of the Co-substituted intact Cu4AMT1 protein. 113Cd(II) NMR studies reveal that the divalent metal site consists of ligands provided by three cysteinyl thiolates and a single histydyl imidazole. The sequence homology between AMT1, ACE1, and MAC1 in the N-terminal 42 residues suggests that ACE1 and MAC1 will, likewise, contain N-terminal Zn modules. A 42-residue ACE1 synthetic peptide gives identical metal binding properties to the corresponding AMT1 synthetic peptide. Thus, AMT1 and likely ACE1 consist of two contiguous modules, residues 1-42 forming an independent Zn(II) module and residues 43-110 enfolding a tetracopper cluster.

Autoactivation by a Candida glabrata copper metalloregulatory transcription factor requires critical minor groove interactions

Rapid transcriptional autoactivation of the Candida glabrata AMT1 copper metalloregulatory transcription factor gene is essential for survival in the presence of high extracellular copper concentrations. Analysis of the interactions between purified recombinant AMT1 protein and the AMT1 promoter metal regulatory element was carried out by a combination of missing-nucleoside analysis, ethylation interference, site-directed mutagenesis, and quantitative in vitro DNA binding studies. The results of these experiments demonstrate that monomeric AMT1 binds the metal regulatory element with very high affinity and utilizes critical contacts in both the major and minor grooves. A single adenosine residue in the minor groove, conserved in all known yeast Cu metalloregulatory transcription factor DNA binding sites, plays a critical role in both AMT1 DNA binding in vitro and Cu-responsive AMT1 gene transcription in vivo. Furthermore, a mutation in the AMT1 Cu-activated DNA binding domain which converts a single arginine, found in a conserved minor groove binding domain, to lysine markedly reduces AMT1 DNA binding affinity in vitro and results in a severe defect in the ability of C. glabrata cells to mount a protective response against Cu toxicity.

Toxic metal-responsive gene transcription

Metals play a dual role in biological systems, serving as essential co-factors for a wide range of biochemical reactions yet these same metals may be extremely toxic to cells. To cope with the stress of increases in environmental metal concentrations, eukaryotic cells have developed sophisticated toxic metal sensing proteins which respond to elevations in metal concentrations. This signal is transmitted to stimulate the cellular transcriptional machinery to activate expression of metal detoxification and homeostasis genes. This review summarizes our current understanding of the biochemical and genetic mechanisms which underlie cellular responses to toxic metals via metalloregulatory transcription factors.

Analysis of copper-induced metallothionein expression using autonomously replicating plasmids in Candida glabrata

Candida glabrata strains and a stable plasmid were developed that were suitable for analysis of copper-inducible expression from promoters of the three metallothionein (MT) genes. The two homologous MTII genes, MTIIa and MTIIb, encode the same polypeptide but are differentially induced by copper salts. MTIIb is more highly inducible than MTIIa and cells harboring a single MTIIb exhibit a greater resistance to copper salts compared to cells harboring a single MTIIa. The differential copper inducibility was mapped to sequences between -03 and -292 upstream of the MT coding sequences. Expression of MTI is highly Cu-regulated, but this MT gene confers much less resistance than MTII genes.