Aspergillus nidulans nuclear proteins bind to a CCAAT element and the adjacent upstream sequence in the promoter region of the starch-inducible Taka-amylase A gene

Factors regulating cellulolytic gene expression in filamentous fungi: an overview

The growing demand for biofuels such as bioethanol has led to the need for identifying alternative feedstock instead of conventional substrates like molasses, etc. Lignocellulosic biomass is a relatively inexpensive feedstock that is available in abundance, however, its conversion to bioethanol involves a multistep process with different unit operations such as size reduction, pretreatment, saccharification, fermentation, distillation, etc. The saccharification or enzymatic hydrolysis of cellulose to glucose involves a complex family of enzymes called cellulases that are usually fungal in origin. Cellulose hydrolysis requires the synergistic action of several classes of enzymes, and achieving the optimum secretion of these simultaneously remains a challenge. The expression of fungal cellulases is controlled by an intricate network of transcription factors and sugar transporters. Several genetic engineering efforts have been undertaken to modulate the expression of cellulolytic genes, as well as their regulators. This review, therefore, focuses on the molecular mechanism of action of these transcription factors and their effect on the expression of cellulases and hemicellulases.

Research progress on the basic helix-loop-helix transcription factors of Aspergillus species

Basic helix-loop-helix (bHLH) proteins belong to a superfamily of transcription factors, and they are widely distributed in eukaryotic organisms. Members of the bHLH protein family can form homodimers or heterodimers with themselves or other family members, and they often play bifunctional roles as activators and repressors to uniquely regulate the transcription of downstream target genes. The bHLH transcription factors are usually involved in developmental processes, including cellular proliferation and differentiation. Therefore, these transcription factors often play crucial roles in regulating growth, development, and differentiation in eukaryotes. Aspergillus species fungi are widely distributed in the environment, and they play important roles not only in the decomposition of organic matter as an important environmental microorganism but also in the fermentation and the food processing industry. Furthermore, some pathogenic fungi, such as Aspergillus flavus and Aspergillus fumigatus, affect the environment and human health in important ways. Recent research has shown that some Aspergillus bHLH proteins are significantly involved in the regulation of asexual and sexual reproduction, secondary metabolite production, carbohydrate metabolism, conidial and sclerotial production, among other processes. Here, we review the regulatory mechanisms and biological functions of the bHLH transcription factors of the Aspergillus genus to provide a theoretical reference for further study on the growth and development of Aspergillus and the functions of bHLHs.

Development of a promoter shutoff system in Aspergillus oryzae using a sorbitol-sensitive promoter

Promoter shutoff is a general method for analyzing essential genes, but in the fungus Aspergillus oryzae, no tightly repressed promoters have been reported. To overcome the current limitations of conditional promoters, we examined sorbitol- and galactose-responsive genes using microarrays to identify regulatable genes with only minor physiological and genetic effects. We identified two sorbitol-induced genes (designated as sorA and sorB), cloned their promoters, and built a regulated egfp and brlA expression system. Growth medium-dependent enhanced green fluorescence protein (EGFP) fluorescence and conidiation were confirmed for egfp and brlA under the control of their respective promoters. We also used this shutoff system to regulate the essential rhoA, which demonstrated the expected growth inhibition under repressed growth conditions. Our new sorbitol promoter shutoff system developed can serve as a valuable new tool for essential gene analyses of filamentous fungi.

Gel mobility shift scanning of pectin-inducible promoter from Penicillium griseoroseum reveals the involvement of a CCAAT element in the expression of a polygalacturonase gene

Previous reports have described pgg2, a polygalacturonase-encoding gene of Penicillium griseoroseum, as an attractive model for transcriptional regulation studies, due to its high expression throughout several in vitro growth conditions, even in the presence of non-inducing sugars such as sucrose. A search for regulatory motifs in the 5' upstream regulatory sequence of pgg2 identified a putative CCAAT box that could justify this expression profile. This element, located 270 bp upstream of the translational start codon, was tested as binding target for regulatory proteins. Analysis of a 170 bp promoter fragment by electrophoretic mobility shift assay (EMSA) with nuclear extracts prepared from mycelia grown in pectin-containing culture medium revealed a high mobility complex that was subsequently confirmed by analyzing it with a double-stranded oligonucleotide spanning the CCAAT motif. A substitution in the core sequence for GTAGG partially abolished the formation of specific complexes, showing the involvement of the CCAAT box in the regulation of the polygalacturonase gene studied.

Study on the molecular basis of glucoamylase overproduction of a mutant strainAspergillus niger T21

The molecular basis for increasing of the glucoamylase (GLA) production of anAspergillus niger mutant T21 was investigated. Northern blot analysis showed that the amount ofglaA specific mRNA ofA. niger T21 was about 20 times higher than that of its start strainA. niger AS 3.795. The twoglaA promoter fusions (PglaA)-uidAs were respectively introduced intoA. niger. Analysis of GUS activity of the transformants revealed that thePglaA activity of the strain T21 is about 3 times stronger than that of the strain AS 3.795. It is considered to be one of the reasons for the increase ofglaA transcriptional level in the strain T21. However, comparing with the 20 times increase in the amount of glaA mRNA the alteration oftrans regulation should be the most important reason for that. The results of deletion analysis of 5'-c/s region ofA. niger T21glaA gene indicated that the region from-408 to-513 bp upstream of ATG is responsible for the high level expression ofglaA.

Improvement of the secretion of extracellular proteins and isolation and characterization of the amylase I (amy1) gene from Ophiostoma floccosum

UV mutagenesis was applied to improve protein secretion in Ophiostoma floccosum. Amylase activity was used as an indicator for enhanced protein production after repeated rounds of mutagenic treatment. The amylase activity in the culture supernatant of the best mutant (MQ.5.1) was increased by more than 240-fold compared to the initial parental strain. At the same time, the increase in total secreted protein was about six times greater than the parental strain. Secreted proteinase and lipase activities of the parental strain and four key mutants were also investigated. N-terminal sequencing of the five dominant protein bands separated by SDS-PAGE from the culture supernatant was conducted. Two of the proteins identified were subtilisin-like proteinases and one was a pepsin-like proteinase. In addition, one protein was identified as an alpha-amylase and one remained unidentified. A 6.5 kb DNA fragment was isolated by Genomic Walking PCR using primers based on the alpha-amylase amino acid sequence. The amplified fragment contained the entire gene encoding alpha-amylase (amy1) and its regulatory sequences. Analysis showed that multiple transcripts were generated from the single alpha-amylase gene locus.

Activation of zoosporogenesis-specific genes in Phytophthora infestans involves a 7-nucleotide promoter motif and cold-induced membrane rigidity

Infections of plants by the oomycete Phytophthora infestans typically result from zoospores, which develop from sporangia at cold temperatures. To help understand the relevant cold-induced signaling pathway, factors regulating the transcription of the zoosporogenesis-specific NIF (nuclear LIM-interactor-interacting factor) gene family were examined. Sequences required for inducing PinifC3 were identified by analyzing truncated and mutated promoters using the beta-glucuronidase reporter in stable transformants. A 7-nucleotide (nt) sequence located 139 bases upstream of the major transcription start point (GGACGAG) proved essential for the induction of PinifC3 when sporangia were shifted from ambient to cold temperatures. The motif, named the cold box, also conferred cold inducibility to a promoter normally activated only during sexual development. An identical motif was detected in the two other zoosporogenesis-specific NIF genes from P. infestans and three Phytophthora sojae orthologues, and a closely related sequence was found in Phytophthora ramorum orthologues. The 7-nt motif was also found in the promoters of other zoosporogenesis-induced genes. The presence of a cold box-interacting protein in nuclear extracts of P. infestans sporangia was demonstrated using electrophoretic mobility shift assays. Furthermore, zoospore release and cold box-regulated transcription were stimulated by the membrane rigidizer dimethyl sulfoxide and inhibited by the membrane fluidizer benzyl alcohol. The data therefore delineate a pathway in which sporangia perceive cold temperatures through membrane rigidity, which activates signals that drive both zoosporogenesis and cold-box-mediated transcription.

Isolation of genes encoding novel transcription factors which interact with the Hap complex from Aspergillus species

The Saccharomyces cerevisiae CCAAT-binding factor is composed of four subunits Hap2p, Hap3p, Hap4p and Hap5p. Three subunits, Hap2/3/5p, are required for DNA-binding and Hap4p is involved in transcriptional activation. Although homologues of Hap2/3/5p (in the case of Aspergillus nidulans; HapB/C/E, respectively) were found in many eukaryotes, no Hap4p homologues have been found except for the other yeast, Kluyveromyces lactis. With the lexA-hap2, -hapB, -hapC, or -hapE fusion gene, we evaluated the ability of interaction between Aspergillus Hap subunits and S. cerevisiae Hap4p subunit in S. cerevisiae. Using the system with lexA-hapB, a gene encoding a novel transcriptional activator, which interacted with the Hap complex, was isolated from A. nidulans and designated hapX.

Upward shift of the pH optimum of Acremonium ascorbate oxidase

A gene encoding a thermostable Acremonium ascorbate oxidase (ASOM) was randomly mutated to generate mutant enzymes with altered pH optima. One of the mutants, which exhibited a significantly higher activity in the pH range 4.5-7 compared to ASOM, had a Gln183Arg substitution in the region corresponding to SBR1, one of the substrate binding regions of the zucchini enzyme. The other mutant with almost the same pH profile as Gln183Arg had a Thr527Ala substitution near the type 3 copper center and became more sensitive to azide than ASOM. Site-directed mutagenesis in the substrate binding regions with reference to the amino acid sequences of plant enzymes led to isolation of mutants shifted upward in the pH optimum; Val193Pro and Val193Pro/Pro190Ile increased the pH optimum by 1 and 0.5 units, respectively, while retaining the near-wild-type thermostability and azide sensitivity. The homology model of ASOM constructed from the zucchini enzyme coordinates suggested that replacement of Val193 by Pro could disturb the ion pair networks among Arg309, Glu192, Arg194 and Glu311. This perturbation could affect either the molecular recognition between the substrate and ASOM or the electron transfer from the substrate to the type 1 copper center, leading to the alkaline shift of the catalytic activity of the mutant enzyme. The other mutations, Val193Pro/Pro190Ile, could also induce similar structural perturbations involving the ion pair networks.

A transcriptional activator, AoXlnR, controls the expression of genes encoding xylanolytic enzymes in Aspergillus oryzae

By deletion across the promoter region of the xynF1 gene encoding the major Aspergillus oryzae xylanase, a 53-bp DNA fragment containing the XlnR binding sequence GGCTAAA as well as two similar sequences was shown to confer xylan inducibility on the gene. Complementary and genomic DNAs encoding the Aspergillus niger xlnR homologous gene, abbreviated AoxlnR, were cloned from A. oryzae and sequenced. AoXlnR comprised 971 amino acids with a zinc binuclear cluster domain at the N-terminal region and revealed 77.5% identity to the A. niger XlnR. Recombinant AoXlnR protein encompassing the zinc cluster region of the N-terminal part bound to both the consensus binding sequence and its cognate sequence, GGCTGA, with an approximately 10 times lower affinity. GGCTA/GA is more appropriate as the XlnR consensus binding sequence. Both sequences functioned independently in vivo in XlnR-mediating induction of the xynF1 gene. This was further confirmed by using an AoxlnR disruptant. Neither the xynF1 nor the xylA gene was expressed in the disruptant, suggesting that the xylan-inducible genes in A. oryzae may also be controlled in the same manner as described for A. niger.

A quantity control mechanism regulating levels of the HapE subunit of the Hap complex in Aspergillus nidulans: no accumulation of HapE in hapC deletion mutants

The Aspergillus nidulans CCAAT-binding complex (Hap complex) consists of at least three subunits, HapB, HapC and HapE. To investigate the quantity control mechanisms of the subunits during assembly of the Hap complex, reconstitution studies with the recombinant subunits and extracts prepared from the respective hap subunit deletion mutants were carried out. Furthermore, Western blot analysis of the Hap subunits and Northern blot analysis of the hap genes with the respective deletion mutants were also performed. From all the results together, it was suggested that the number of the HapC molecule could adjust that of the HapE molecule by forming stable heterodimers prior to assembly of the Hap complex.

Aspergillus enzymes involved in degradation of plant cell wall polysaccharides

Degradation of plant cell wall polysaccharides is of major importance in the food and feed, beverage, textile, and paper and pulp industries, as well as in several other industrial production processes. Enzymatic degradation of these polymers has received attention for many years and is becoming a more and more attractive alternative to chemical and mechanical processes. Over the past 15 years, much progress has been made in elucidating the structural characteristics of these polysaccharides and in characterizing the enzymes involved in their degradation and the genes of biotechnologically relevant microorganisms encoding these enzymes. The members of the fungal genus Aspergillus are commonly used for the production of polysaccharide-degrading enzymes. This genus produces a wide spectrum of cell wall-degrading enzymes, allowing not only complete degradation of the polysaccharides but also tailored modifications by using specific enzymes purified from these fungi. This review summarizes our current knowledge of the cell wall polysaccharide-degrading enzymes from aspergilli and the genes by which they are encoded.

Regulation of the amylolytic and (hemi-)cellulolytic genes in aspergilli

Filamentous fungi produce high levels of polysaccharide-degrading enzymes and are frequently used for the production of industrial enzymes. Because of the high secretory capacity for enzymes, filamentous fungi are effective hosts for the production of foreign proteins. Genetic studies with Aspergillus nidulans have shown pathway-specific regulatory systems that control a set of genes that must be expressed to catabolize particular substrates. Besides the pathway-specific regulation, wide domain regulatory systems exist that affect a great many individual genes in different pathways. A molecular analysis of various regulated systems has confirmed the formal models derived from purely genetic data. In general, many genes are subject to more than one regulatory system. In this article, we describe two transcriptional activators, AmyR and XlnR, and an enhancer, Hap complex, in view of their regulatory roles in the expression of the amylolytic and (hemi-)cellulolytic genes mainly in aspergilli. The amyR gene has been isolated as a transcriptional activator involved in the expression of amylolytic genes from A. oryzae, A. niger, and A. nidulans, and the xlnR gene, which has been isolated from A. niger and A. oryzae, activates the expression of xylanolytic genes as well as some cellulolytic genes in aspergilli. Both AmyR and XlnR have a typical zinc binuclear cluster DNA-binding domain at their N-terminal regions. Hap complex, a CCAAT-binding complex, enhances the overall promoter activity and increases the expression levels of many fungal genes, including the Taka-amylase A gene. Hap complex comprises three subunits, HapB, HapC, and HapE, in A. nidulans and A. oryzae as well as higher eukaryotes, whereas HAP complex in Saccharomyces cerevisiae and Kluyveromyces lactis has the additional subunit, Hap4p, which is responsible for the transcriptional activation. Hap complex is suggested to enhance transcription by remodeling the chromatin structure. The regulation of gene expression in filamentous fungi of industrial interest could follow basically the same general principles as those discovered in A. nidulans. The knowledge of regulation of gene expression in combination with traditional genetic techniques is expected to be increasingly utilized for strain breeding. Furthermore, this knowledge provides a basis for the rational application of transcriptional regulators for biotechnological processes in filamentous fungi.

HAP-Like CCAAT-binding complexes in filamentous fungi: implications for biotechnology

Regulatory CCAAT boxes are found frequently in eukaryotic promoter regions. They are bound by different CCAAT-binding factors. Until now, a single CCAAT-binding complex has been reported in fungi. It is also found in higher eukaryotes and is highly conserved among eukaryotic organisms. This multimeric protein complex is designated HAP, AnCF, CBF, or NF-Y. The complex consists of at least three subunits. In fungi, only the HAP complex of Saccharomyces cerevisiae had been known for a long time. The recent cloning of genes encoding the components of the corresponding complex (AnCF/PENR1) of Aspergillus nidulans and characterization of CCAAT-regulated genes in A. nidulans, as well as other filamentous fungi, led to a deeper insight into the role of this transcription complex, in particular in aerobically growing fungi. An overview of the function of HAP-like complexes in gene regulation in filamentous fungi is presented. Some of the genes that have been found to be regulated by HAP-like complexes encode enzymes of biotechnological interest, like taka-amylase, xylanases, cellobiohydrolase, and penicillin biosynthesis enzymes. The importance of HAP-like complexes in controlling the expression of biotechnologically important genes is discussed.

Structure and expression properties of the endo-beta-1,4-glucanase A gene from the filamentous fungus Aspergillus nidulans

Endo-beta-1,4-glucanase A (EG A) of Aspergillus nidulans was purified to homogeneity, and its genomic gene (eglA) was cloned based on partial amino acid sequences of the purified enzyme and sequenced. The eglA gene comprised 1228 bp with four putative introns and encoded a polypeptide of 326 amino acids bearing high homology to the family A cellulases. The eglA promoter activity in A. nidulans was examined using the A. oryzae Taka-amylase A gene as a reporter. Expression of the reporter gene was induced by carboxymethylcellulose and cellobiose, and repressed by glucose, galactose, mannose, xylose, sorbitol, glycerol and succinate. Lactose neither induced nor repressed the expression.

Depression of the xylanase-encoding cgxA gene of Chaetomium gracile in Aspergillus nidulans

Regulation of the Chaetomium gracile xylanase A gene (cgxA) was investigated using Aspergillus nidulans as an intermediate host. Deletion of a 185 bp DNA fragment from its promoter region led to higher levels of the cgxA gene expression, indicating that the 185 bp DNA fragment contains an element involved in repression of the gene. A nuclear extract was assayed for proteins which bind to the 185 bp DNA fragment. A protein designated AnRP bound sequence specifically to the DNA fragment. The minimum sequence required for AnRP binding, 5'TTGACAAAT-3', was determined by means of gel mobility shift assays with various double-stranded oligonucleotides. Furthermore, this sequence repressed the expression of the cgxA gene when inserted at the 5' end of the cgxA gene on pXAH, which was deleted for the repressive element from the promoter region.

AnCF, the CCAAT binding complex of Aspergillus nidulans, contains products of the hapB, hapC, and hapE genes and is required for activation by the pathway-specific regulatory gene amdR

CCAAT binding factors (CBFs) positively regulating the expression of the amdS gene (encoding acetamidase) and two penicillin biosynthesis genes (ipnA and aatA) have been previously found in Aspergillus nidulans. The factors were called AnCF and PENR1, respectively. Deletion of the hapC gene, encoding a protein with significant similarity to Hap3p of Saccharomyces cerevisiae, eliminated both AnCF and PENR1 binding activities. We now report the isolation of the genes hapB and hapE, which encode proteins with central regions of high similarity to Hap2p and Hap5p of S. cerevisiae and to the CBF-B and CBF-C proteins of mammals. An additional fungus-specific domain present in HapE was revealed by comparisons with the homologs from S. cerevisiae, Neurospora crassa, and Schizosaccharomyces pombe. The HapB, HapC, and HapE proteins have been shown to be necessary and sufficient for the formation of a CCAAT binding complex in vitro. Strains with deletions of each of the hapB, hapC, and hapE genes have identical phenotypes of slow growth, poor conidiation, and reduced expression of amdS. Furthermore, induction of amdS by omega amino acids, which is mediated by the AmdR pathway-specific activator, is abolished in the hap deletion mutants, as is growth on gamma-aminobutyric acid as a sole nitrogen or carbon source. AmdR and AnCF bind to overlapping sites in the promoters of the amdS and gatA genes. It is known that AnCF can bind independently of AmdR. We suggest that AnCF binding is required for AmdR binding in vivo.

Cloning of a thermostable ascorbate oxidase gene from Acremonium sp. HI-25 and modification of the azide sensitivity of the enzyme by site-directed mutagenesis

A gene encoding a thermostable ascorbate oxidase (ASOM) was cloned from Acremonium sp. HI-25 and sequenced. The gene comprised 1709 bp and was interrupted by a single intron of 57 bp. ASOM consisted of 551 amino acids including a signal peptide with a molecular mass of 61200, and contained four histidine-rich regions with high sequence homology to the corresponding regions of other multicopper oxidases. The ASOM gene was expressed in Aspergillus nidulans under the Aspergillus oryzae Taka-amylase A gene promoter. The recombinant enzyme (An-ASOM) exhibited almost the same enzymatic properties as ASOM. The ASOM gene was mutated by site-directed mutagenesis with reference to the amino acid sequences of plant enzymes to generate enzymes with altered azide sensitivity. Site-directed mutagenesis at the trinuclear active copper site resulted in an increase in azide resistance; the Ala465Leu and Phe463Trp/Ala465Leu mutants exhibited approximately 10 and 20% increases in azide resistance, respectively.

The two genes encoding starch-branching enzymes IIa and IIb are differentially expressed in barley

The sbeIIa and sbeIIb genes, encoding starch-branching enzyme (SBE) IIa and SBEIIb in barley (Hordeum vulgare L.), have been isolated. The 5' portions of the two genes are strongly divergent, primarily due to the 2064-nucleotide-long intron 2 in sbeIIb. The sequence of this intron shows that it contains a retro-transposon-like element. Expression of sbeIIb but not sbeIIa was found to be endosperm specific. The temporal expression patterns for sbeIIa and sbeIIb were similar and peaked around 12 d after pollination. DNA gel-blot analysis demonstrated that sbeIIa and sbeIIb are both single-copy genes in the barley genome. By fluorescence in situ hybridization, the sbeIIa and sbeIIb genes were mapped to chromosomes 2 and 5, respectively. The cDNA clones for SBEIIa and SBEIIb were isolated and sequenced. The amino acid sequences of SBEIIa and SBEIIb were almost 80% identical. The major structural difference between the two enzymes was the presence of a 94-amino acid N-terminal extension in the SBEIIb precursor. The (beta/alpha)8-barrel topology of the alpha-amylase superfamily and the catalytic residues implicated in branching enzymes are conserved in both barley enzymes.

Molecular regulation of beta-lactam biosynthesis in filamentous fungi

The most commonly used beta-lactam antibiotics for the therapy of infectious diseases are penicillin and cephalosporin. Penicillin is produced as an end product by some fungi, most notably by Aspergillus (Emericella) nidulans and Penicillium chrysogenum. Cephalosporins are synthesized by both bacteria and fungi, e.g., by the fungus Acremonium chrysogenum (Cephalosporium acremonium). The biosynthetic pathways leading to both secondary metabolites start from the same three amino acid precursors and have the first two enzymatic reactions in common. Penicillin biosynthesis is catalyzed by three enzymes encoded by acvA (pcbAB), ipnA (pcbC), and aatA (penDE). The genes are organized into a cluster. In A. chrysogenum, in addition to acvA and ipnA, a second cluster contains the genes encoding enzymes that catalyze the reactions of the later steps of the cephalosporin pathway (cefEF and cefG). Within the last few years, several studies have indicated that the fungal beta-lactam biosynthesis genes are controlled by a complex regulatory network, e. g., by the ambient pH, carbon source, and amino acids. A comparison with the regulatory mechanisms (regulatory proteins and DNA elements) involved in the regulation of genes of primary metabolism in lower eukaryotes is thus of great interest. This has already led to the elucidation of new regulatory mechanisms. Furthermore, such investigations have contributed to the elucidation of signals leading to the production of beta-lactams and their physiological meaning for the producing fungi, and they can be expected to have a major impact on rational strain improvement programs. The knowledge of biosynthesis genes has already been used to produce new compounds.

The molecular biology of secreted enzyme production by fungi

Enzymes from filamentous fungi are already widely exploited, but new applications for known enzymes and new enzymic activities continue to be found. In addition, enzymes from less amenable non-fungal sources require heterologous production and fungi are being used as the production hosts. In each case there is a need to improve production and to ensure quality of product. While conventional, mutagenesis-based, strain improvement methods will continue to be applied to enzyme production from filamentous fungi the application of recombinant DNA techniques is beginning to reveal important information on the molecular basis of fungal enzyme production and this knowledge is now being applied both in the laboratory and commercially. We review the current state of knowledge on the molecular basis of enzyme production by filamentous fungi. We focus on transcriptional and post-transcriptional regulation of protein production, the transit of proteins through the secretory pathway and the structure of the proteins produced including glycosylation.

Molecular regulation of penicillin biosynthesis in Aspergillus (Emericella) nidulans

The beta-lactam antibiotic penicillin is produced as end product by only some filamentous fungi, most notably by Aspergillus nidulans and Penicillium chrysogenum. The biosynthesis of this secondary metabolite is catalyzed by three enzymes which are encoded by the following three genes: acvA (pcbAB), ipnA (pcbC) and aat (penDE). The genes are organized into a gene cluster. In A. nidulans, several studies have indicated that the genes are controlled by a complex regulatory network. The wide-domain regulatory protein PACC binds to the intergenic region between acvA and ipnA and, at alkaline pH, increases at least ipnA gene transcription. An additional DNA binding protein (PENR1) was suggested to repress acvA and to activate ipnA and aat expression. Furthermore, three recessive trans-acting mutations have been characterized (prgA1, prgB1, npeE1) which most likely correspond to positively acting regulatory genes of the penicillin biosynthesis genes.

Identification of a major cis-acting DNA element controlling the bidirectionally transcribed penicillin biosynthesis genes acvA (pcbAB) and ipnA (pcbC) of Aspergillus nidulans

The beta-lactam antibiotic penicillin is produced as a secondary metabolite by some filamentous fungi. In this study, the molecular regulation of the Aspergillus (Emericella) nidulans penicillin biosynthesis genes acvA (pcbAB) and ipnA (pcbC) was analyzed. acvA and ipnA are divergently oriented and separated by an intergenic region of 872 bp. Translational fusions of acvA and ipnA with the two Escherichia coli reporter genes lacZ and uidA enabled us to measure the regulation of both genes simultaneously. A moving-window analysis of the 872-bp intergenic region indicated that the divergently oriented promoters are, at least in part, overlapping and share common regulatory elements. Removal of nucleotides -353 to -432 upstream of the acvA gene led to a 10-fold increase of acvA-uidA expression and simultaneously to a reduction of ipnA-lacZ expression to about 30%. Band shift assays and methyl interference analysis using partially purified protein extracts revealed that a CCAAT-containing DNA element within this region was specifically bound by a protein (complex), which we designated PENR1, for penicillin regulator. Deletion of 4 bp within the identified protein binding site caused the same contrary effects on acvA and ipnA expression as observed for all of the deletion clones which lacked nucleotides -353 to -432. The PENR1 binding site thus represents a major cis-acting DNA element. The intergenic regions of the corresponding genes of the beta-lactam-producing fungi Penicillium chrysogenum and Acremonium chrysogenum also diluted the complex formed between the A. nidulans probe and PENR1 in vitro, suggesting that these beta-lactam biosynthesis genes are regulated by analogous DNA elements and proteins.

The hapC gene of Aspergillus nidulans is involved in the expression of CCAAT-containing promoters

The 5' regulatory region of the amdS gene of Aspergillus nidulans, which encodes an acetamidase required for growth on acetamide as a carbon and nitrogen source, contains a CCAAT sequence which is required for setting the basal level of amdS expression. Mobility shift studies have identified a factor in A. nidulans nuclear extracts which binds to this CCAAT sequence. In Saccharomyces cerevisiae the HAP3 gene encodes one component of a multisubunit complex that binds CCAAT sequences. A search of the EMBL and SwissProt databases has revealed an A. nidulans sequence with significant homology to the HAP3 gene adjacent to the previously cloned regulatory gene amdR. Sequencing of the remainder of this region has confirmed the presence of a gene, designated hapC, with extensive homology to HAP3. The predicted amino acid sequence of HapC shows extensive identity to HAP3 in the central conserved domain, but shows little conservation in the flanking sequences. A haploid carrying a hapC deletion has been created and is viable, but grows poorly on all media tested. This null mutant grows especially slowly on acetamide as a sole carbon and nitrogen source, indicating that hapC plays a role in amdS expression. In agreement with this notion, it has been shown that the hapC deletion results in reduced levels of expression of an amdS::lacZ reporter gene and this effect is particularly evident under conditions of carbon limitation. Nuclear extracts prepared from the hapC deletion mutant show no CCAAT binding activity to the amdS or gatA promoters, indicating that hapC may encode a component of the complex binding at this sequence.

The Aspergillus nidulans penicillin-biosynthesis gene aat (penDE) is controlled by a CCAAT-containing DNA element

Analysis of the promoter of the penicillin biosynthesis aat (penDE) gene of Aspergillus nidulans using band-shift assays led to the identification of a CCAAT-containing DNA element which was specifically bound by a protein (complex). The identified DNA element was localised about 250 bp upstream of the transcriptional-start sites of aat. Substitution of the CCAAT core sequence by GATCC led to a fourfold reduction of expression of an aat-lacZ gene fusion. The identified binding site thus was functional in vivo and positively influenced at expression. Partial purification of the CCAAT binding protein and cross-competition experiments provided evidence that the binding protein is identical to the identified putative penicillin-regulatory protein PENR1, binding to the CCAAT element in the bidirectional intergenic promoter region between acvA (pcbAb) and ipnA (pcbC). Hence, PENR1 seems to be involved in the regulation of all three penicillin-biosynthesis genes. Cross-competition experiments demonstrated that the promoter region of the corresponding aat (penDE) gene of Penicillium chrysogenum was capable to dilute the shift of the A. nidulans probe with PENR1, suggesting the presence of a similar regulatory mechanism in this fungus. Taken together with previous data, CCAAT-containing DNA elements thus seem to represent major cis-acting sites in the promoters of beta-lactam-biosynthesis genes.

Two family G xylanase genes from Chaetomium gracile and their expression in Aspergillus nidulans

With oligonucleotides based on the amino-terminal and internal amino-acid sequences of a xylanase, two xylanase genes, cgxA and cgxB, were isolated and sequenced from Chaetomium gracile wild and mutant strains. Each gene isolated from both strains was essentially the same as far as nucleotide sequences were compared. The mature CgXA and CgXB xylanases comprise 189 and 211 amino acids, respectively, and share 68.5% homology. The CgXA was found to be the major enzyme in the mutant strain. Comparison of these amino-acid sequences with xylanase sequences from other origins showed that they have a high degree of identity to the family G xylanases. The cgxA and cgxB genes were introduced into Aspergillus nidulans and found to be expressed with their own promoters.

Yeast proteins can activate expression through regulatory sequences of the amdS gene of Aspergillus nidulans

The upstream regulatory region of the amdS gene of Aspergillus nidulans contains a CCAAT sequence known to be important in setting both basal and depressed levels of expression. We have investigated whether the CCAAT-binding HAP2/3/4 complex of the yeast Saccharomyces cerevisiae can recognise this sequence in an amdS context. Sequences from the 5' region of amdS were cloned in front of the CYC1-lacZ fusion gene bearing a minimal promoter and transformed into wild-type and hap2 strains of yeast. This study has indicated that amdS sequences are capable of promoting regulated expression of the fusion gene in response to carbon limitation. The yeast HAP2/3/4 complex can recognise the amdS CCAAT sequence and activate expression from this sequence. In addition, the results indicate that other yeast proteins can also regulate expression from the A. nidulans amdS 5'sequences under carbon-limiting conditions.

The effect of multiple copies of the upstream region on expression of the Aspergillus niger glucoamylase-encoding gene

The regulation of transcription of the glucoamylase-encoding gene (glaA) of Aspergillus niger was studied. To facilitate this study a reporter strain containing a fusion of the glaA promoter (PglaA) of A. niger to the beta-glucuronidase-encoding gene (uidA) of Escherichia coli was constructed. To analyze whether regulatory proteins are involved in the regulation of glaA, multiple copies of PglaA were introduced into this reporter strain. Analysis of the resulting strains revealed that introduction of an increasing number of PglaA copies resulted in lower expression of the uidA reporter gene and the endogenous glaA gene in cultures cultivated on different inducing carbon sources. However, repression by xylose was not influenced by the copy number of PglaA. These results indicate that the expression of genes under control of PglaA are regulated by specific trans-acting regulatory protein(s). Deletion analysis of PglaA indicated that regulatory proteins interact with DNA sequences within 0.5-kb upstream from the ATG, whereas sequences between about 0.8- and 0.5-kb upstream from the ATG are required for high-level expression of glaA.