The Aspergillus nidulans metZ gene encodes a transcription factor involved in regulation of sulfur metabolism in this fungus and other Eurotiales.

In Aspergillus nidulans, expression of sulfur metabolism genes is activated by the MetR transcription factor containing a basic region and leucine zipper domain (bZIP). Here we identified and characterized MetZ, a new transcriptional regulator in A. nidulans and other Eurotiales.

Regulatory mutations affecting sulfur metabolism induce environmental stress response in Aspergillus nidulans.

Mutations in the cysB, sconB and sconC genes affect sulfur metabolism in Aspergillus nidulans in different ways. The cysB mutation blocks synthesis of cysteine by the main pathway and leads to a shortage of this amino acid. The sconB and sconC mutations affect subunits of the SCF ubiquitin ligase complex, which inactivates the MetR transcription factor in the presence of an excess of cysteine.

Novel mutations reveal two important regions in Aspergillus nidulans transcriptional activator MetR.

Expression of the sulfur assimilation pathway in Aspergillus nidulans is under control of sulfur metabolite repression, which is composed of scon genes encoding subunits of ubiquitin ligase and the metR gene coding for a transcriptional activator. In this paper we report three dominant suppressors of methionine requirement isolated from a metB3 diploid strain. All three mutations lead to the substitution of phenylalanine 48 by serine or leucine in the conserved N-terminal region of the MetR protein.

Sulfate permeasesphylogenetic diversity of sulfate transport.

Sulfate uptake, the first step of sulfate assimilation in all organisms, is a highly endoergic, ATP requiring process. It is under tight control at the transcriptional level and is additionally modulated by posttranslational modifications, which are not yet fully characterized. Sulfate anion is taken up into the cell by specific transporters, named sulfate permeases, located in the cell membrane.

Aspergillus nidulans genes encoding reverse transsulfuration enzymes belong to homocysteine regulon.

Homocysteine is an intermediate in methionine synthesis in Aspergillus nidulans, but it can also be converted to cysteine by the reverse transsulfuration pathway involving cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CGL). Because homocysteine is toxic to the cell at high concentrations, this pathway also functions as a means of removal of its excess. We found that the transcription of the mecA and mecB genes encoding CBS and CGL was upregulated by excess of homocysteine as well as by shortage of cysteine.

The Aspergillus nidulans pigP gene encodes a subunit of GPI-N-acetylglucosaminyltransferase which influences filamentation and protein secretion.

Glycosylphosphatidylinositol (GPI) anchoring is the main mechanism allowing proper localization of secretory proteins in cell membranes. We have isolated an Aspergillus nidulans homolog of the human PIG-P gene, which encodes a subunit of acetylglucosaminyltransferase (GPI-GnT)-an enzyme involved in the synthesis of GPI anchors. A.

The 2008 update of the Aspergillus nidulans genome annotation: a community effort.

The identification and annotation of protein-coding genes is one of the primary goals of whole-genome sequencing projects, and the accuracy of predicting the primary protein products of gene expression is vital to the interpretation of the available data and the design of downstream functional applications. Nevertheless, the comprehensive annotation of eukaryotic genomes remains a considerable challenge. Many genomes submitted to public databases, including those of major model organisms, contain significant numbers of wrong and incomplete gene predictions.

The level of sulfane sulfur in the fungus Aspergillus nidulans wild type and mutant strains.

The interdependence of the sulfane sulfur metabolism and sulfur amino acid metabolism was studied in the fungus Aspergillus nidulans wild type strain and in mutants impaired in genes encoding enzymes involved in the synthesis of cysteine (a precursor of sulfane sulfur) or in regulatory genes of the sulfur metabolite repression system. It was found that a low concentration of cellular cysteine leads to elevation of two sulfane sulfurtransferases, rhodanase and cystathionine gamma-lyase, while the level of 3-mercaptopyruvate sulfurtransferase remains largely unaffected. In spite of drastic differences in the levels of biosynthetic enzymes and of sulfur amino acids due to mutations or sulfur supplementation of cultures, the level of total sulfane sulfur is fairly stable.

Multiple fungal enzymes possess cysteine synthase activity in vitro.

We present evidence that there are at least three Aspergillus nidulans enzymes which catalyze in vitro the reaction of O-acetylserine (OAS) with sulfide forming cysteine. This activity is shared by cysteine synthase (CS) encoded by the cysB gene, homocysteine synthase encoded by cysD and by at least one more enzyme. Moreover, arginine, histidine or proline starvation leads to derepression of CS activity even in the cysB,cysD double mutant strains, while neither cysB nor cysD gene transcription is derepressed by amino acid starvation.

Two Aspergillus nidulans genes encoding methylenetetrahydrofolate reductases are up-regulated by homocysteine.

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a co-substrate in the synthesis of methionine from homocysteine. We have cloned and characterized two Aspergillus nidulans genes encoding MTHFRs: metA and metF. Mutations in either gene result in methionine requirement; the metA-encoded enzyme is responsible for only 10-15% of total MTHFR activity.

Sulfate transport in Aspergillus nidulans: a novel gene encoding alternative sulfate transporter.

In Aspergillus nidulans sulfate is taken up by sulfate permease encoded by the sB gene. A unique tight auxotrophic mutant with an impaired promoter region of the sulfate permease gene, sB1(pr), was isolated. Three suppressor genes were cloned by complementation of this mutation.

Transcriptional regulation of methionine synthase by homocysteine and choline in Aspergillus nidulans.

Roles played by homocysteine and choline in the regulation of MS (methionine synthase) have been examined in fungi. The Aspergillus nidulans metH gene encoding MS was cloned and characterized. Its transcription was not regulated by methionine, but was enhanced by homocysteine and repressed by choline and betaine.

The Aspergillus nidulans metR gene encodes a bZIP protein which activates transcription of sulphur metabolism genes.

The identification, isolation and characterization of a new Aspergillus nidulans positive-acting gene metR, which encodes a transcriptional activator of sulphur metabolism, is reported. metR mutants are tight auxotrophs requiring methionine or homocysteine for growth. Mutations in the metR gene are epistatic to mutations in the negative-acting sulphur regulatory scon genes.

Sulphur amino acid synthesis in Schizosaccharomyces pombe represents a specific variant of sulphur metabolism in fungi.

Schizosaccharomyces pombe, in contrast to Saccharomyces cerevisiae and Aspergillus nidulans, lacks cystathionine beta-synthase and cystathionine gamma-lyase, two enzymes in the pathway from methionine to cysteine. As a consequence, methionine cannot serve as an efficient sulphur source for the fungus and does not bring about repression of sulphur assimilation, which is under control of the cysteine-mediated sulphur metabolite repression system. This system operates at the transcriptional level, as was shown for the homocysteine synthase encoding gene.

The Aspergillus nidulans metE gene is regulated by a second system independent from sulphur metabolite repression.

Mutations in the Aspergillus nidulans metE gene lead to requirement for O-acetylhomoserine. The gene was cloned by complementation of the metE31 mutation. The coding sequence was found to be interrupted by two introns of 66 and 50 bp, respectively.

sconC, a gene involved in the regulation of sulphur metabolism in Aspergillus nidulans, belongs to the SKP1 gene family.

sconC, which encodes a negative regulator of sulphur metabolism in Aspergillus nidulans was cloned, sequenced, and found to belong to the highly conserved family of SKP1 genes essential for many cell functions, including cell cycle regulation. The ORF of 722 bp, encoding a protein of 161 amino acids, is interrupted by four introns. There is a fifth intron (135 bp long) in the upstream untranslated sequence.

The Aspergillus nidulans cysA gene encodes a novel type of serine O-acetyltransferase which is homologous to homoserine O-acetyltransferases.

The Aspergillus nidulans cysA gene was cloned by functional complementation of the cysA1 mutation that impairs the synthesis of O:-acetylserine. The molecular nature of cysA1 and cysA103 alleles was characterized; a nucleotide substitution and a frame shift were found in the former and a deletion mutation in the latter. The CYSA protein is 525 amino acids long and is encoded by an uninterrupted open reading frame.

Cloning and characterization of the Kluyveromyces lactis homocysteine synthase gene.

The Kluyveromyces lactis homocysteine synthase gene was cloned by complementation of the Saccharomyces cerevisiae met25 mutation. The coding sequence of the K. lactis gene shows a high similarity to the S.

Cysteine biosynthesis in Saccharomyces cerevisiae: a new outlook on pathway and regulation.

Using a Saccharomyces cerevisiae strain having the activities of serine O-acetyl-transferase (SATase), O-acetylserine/O-acetylhomoserine sulphydrylase (OAS/OAH SHLase), cystathionine beta-synthase (beta-CTSase) and cystathionine gamma-lyase (gamma-CTLase), we individually disrupted CYS3(coding for gamma-CTLase) and CYS4 (coding for beta-CTSase). The obtained gene disruptants were cysteine-dependent and incorporated the radioactivity of (35)S-sulphate into homocysteine but not into cysteine or glutathione. We concluded, therefore, that SATase and OAS/OAH SHLase do not constitute a cysteine biosynthetic pathway and that cysteine is synthesized exclusively through the pathway constituted with beta-CTSase and gamma-CTLase; note that OAS/OAH SHLase supplies homocysteine to this pathway by acting as OAH SHLase.

The metG gene of Aspergillus nidulans encoding cystathionine beta-lyase: cloning and analysis.

The metG gene of Aspergillus nidulans encoding cystathionine beta-lyase, an enzyme of the main pathway of methionine synthesis, was cloned by complementation of a metG mutation. A comparison of metG genomic DNA and a cDNA copy derived from different A. nidulans strains revealed a marked DNA sequence polymorphism manifested mostly by silent point mutations.

Structure and regulation of cysD, the homocysteine synthase gene of Aspergillus nidulans.

The A. nidulans cysD gene encoding homocysteine synthase (O-acetyl-L-homoserine sulphydrylase) has been isolated by functional complementation of a cysD11 mutation. The gene contains five short introns and codes for a protein of 437 amino acids.

The Aspergillus nidulans sulphur regulatory gene sconB encodes a protein with WD40 repeats and an F-box.

The Aspergillus nidulans gene sconB, one of the four identified genes controlling sulphur metabolite repression, was cloned and analysed. It encodes a polypeptide of 678 amino acids containing seven WD repeats characteristic of the large WD40 family of eukaryotic regulatory proteins. The SCONB protein has nuclear localisation signals and is very similar to the Neurospora crassa SCON2 and Saccharomyces cerevisiae Met30 proteins, both of which are involved in the regulation of sulphur metabolism.

Identification of new regulatory genes controlling synthesis of folate-dependent enzymes in Aspergillus nidulans.

Prototrophic revertants of a meth2 strain of aspergillus nidulans which is impaired in the regulation of synthesis of folate-dependent enzymes were isolated and six of them analysed. In three of the isolates reversion was the result of an intragenic suppressor mutation in the metH locus. In the remaining strains suppressor mutations occurred in independent genes.

Cloning and characterization of the Aspergillus nidulans cysB gene encoding cysteine synthase.

The cysB gene of A. nidulans was cloned by complementation of a cysB mutation. This is the first cloned eukaryotic genomic sequence coding for cysteine synthase.

Regulation of sulphate assimilation in Saccharomyces cerevisiae.

We examined how the activity of O-acetylserine and O-acetylhomoserine sulphydrylase (OAS/OAH) SHLase of Saccharomyces cerevisiae is affected by sulphur source added to the growth medium and genetic background of the strain. In a wild-type strain, the activity was repressed if methionine, cysteine or glutathione was added to the growth medium. However, in a strain deficient of cystathionine gamma-lyase, cysteine and glutathione were repressive, but methionine was not.