Loading...
(1/1936) Thaumatin production in Aspergillus awamori by use of expression cassettes with strong fungal promoters and high gene dosage.

Four expression cassettes containing strong fungal promoters, a signal sequence for protein translocation, a KEX protease cleavage site, and a synthetic gene (tha) encoding the sweet protein thaumatin II were used to overexpress this protein in Aspergillus awamori lpr66, a PepA protease-deficient strain. The best expression results were obtained with the gdhA promoter of A. awamori or with the gpdA promoter of Aspergillus nidulans. There was good correlation of tha gene dosage, transcript levels, and thaumatin secretion. The thaumatin gene was expressed as a transcript of the expected size in each construction (1.9 or 1.4 kb), and the transcript levels and thaumatin production rate decayed at the end of the growth phase, except in the double transformant TB2b1-44-GD5, in which secretion of thaumatin continued until 96 h. The recombinant thaumatin secreted by a high-production transformant was purified to homogeneity, giving one major component and two minor components. In all cases, cleavage of the fused protein occurred at the KEX recognition sequence. This work provides new expression systems in A. awamori that result in very high levels of thaumatin production.  (+info)

(2/1936) Identification and characterization of genes required for hyphal morphogenesis in the filamentous fungus Aspergillus nidulans.

In the filamentous fungus Aspergillus nidulans, germination of an asexual conidiospore results in the formation of a hyphal cell. A key feature of spore germination is the switch from isotropic spore expansion to polarized apical growth. Here, temperature-sensitive mutations are used to characterize the roles of five genes (sepA, hypA, podB-podD) in the establishment and maintenance of hyphal polarity. Evidence that suggests that the hypA, podB, and sepA genes are required for multiple aspects of hyphal morphogenesis is presented. Notably, podB and sepA are needed for organization of the cytoskeleton at sites of polarized growth. In contrast, podC and podD encode proteins that appear to be specifically required for the establishment of hyphal polarity during spore germination. The role of sepA and the pod genes in controlling the spatial pattern of polarized morphogenesis in germinating spores is also described. Results obtained from these experiments indicate that the normal pattern of germ-tube emergence is dependent upon the integrity of the actin cytoskeleton.  (+info)

(3/1936) Cloning and expression of a cDNA encoding the laccase from Schizophyllum commune.

We cloned and analyzed the nucleotide sequence of a cDNA that encodes polyphenol oxidase (laccase) from the white-rot basidiomycete Schizophyllum commune. The nucleotide sequence of the full-length cDNA contained a 1554-base open reading frame that encoded a polypeptide of 518 amino acid residues, including a putative signal peptide of 16 residues. It contained four highly similar regions that are conserved in the deduced amino acid sequences of other laccases, including the region thought to be involved in copper binding. Aspergillus sojae strain 1860 (which has low protease levels) was transformed with the plasmid lacAL/pTPT, which contained the laccase gene under the control of the tannase promoter from Aspergillus oryzae. Laccase was secreted into the medium when transformants A1 and A2 were cultured in tannic acid-containing medium.  (+info)

(4/1936) Purification and characterization of Aspergillus ficuum endoinulinase.

Endoinulinase from Aspergillus ficuum, which catalyzes the hydrolysis of inulin via an endo-cleavage mode, was purified by chromatography from Novozym 230 as a starting commercial enzyme mixture on CM-Sephadex and DEAE-Sepharose, and by preparative electrophoresis under native conditions. The enzyme was estimated to be pure on the basis of its I/S ratio, whose value was infinite in our assay conditions. Two forms separated by using this method. SDS gel electrophoresis showed the two purified forms to respectively exhibit molecular weights of 64,000 +/- 500 and 66,000 +/- 1,000. The results of deglycosylation indicated that the two forms were originally the same protein but with different sugar contents. A molecular weight of 54,800 +/- 1,500 was found by gel filtration of the native enzyme, indicating the native functional protein to be a monomer. The enzyme showed nearly absolute substrate specificity towards inulin and inulooligosaccharides, and acted via an endo-attack to produce mainly inulotriose during the late stage of the reaction. The apparent Km and Vmax values for inulin hydrolysis were 8.1 +/- 1.0 mM and 773 +/- 60 U/mg, respectively. The internal peptides of the enzyme showed sequence homology to the endoinulinase of Penicillium purpurogenum.  (+info)

(5/1936) Deficiency of the hematopoietic cell-specific Rho family GTPase Rac2 is characterized by abnormalities in neutrophil function and host defense.

In mammals, the Rho family GTPase Rac2 is restricted in expression to hematopoietic cells, where it is coexpressed with Rac1. Rac2-deficient mice were created to define the physiological requirement for two near-identical Rac proteins in hematopoietic cells. rac2-/- neutrophils displayed significant defects in chemotaxis, in shear-dependent L-selectin-mediated capture on the endothelial substrate Glycam-1, and in both F-actin generation and p38 and, unexpectedly, p42/p44 MAP kinase activation induced by chemoattractants. Superoxide production by rac2-/- bone marrow neutrophils was significantly reduced compared to wild type, but it was normal in activated peritoneal exudate neutrophils. These defects were reflected in vivo by baseline neutrophilia, reduced inflammatory peritoneal exudate formation, and increased mortality when challenged with Aspergillus fumigatus. Rac2 is an essential regulator of multiple specialized neutrophil functions.  (+info)

(6/1936) Production of specific monoclonal antibodies to Aspergillus species and their use in immunohistochemical identification of aspergillosis.

Two anti-Aspergillus murine monoclonal antibodies (MAbs), designated 164G and 611F, have been produced; both specifically recognize cytoplasmic antigens of A. fumigatus, A. flavus, and A. niger by enzyme-linked immunosorbent assay. The MAbs can identify Aspergillus spp. both in frozen sections by immunofluorescence and in paraffin-embedded clinical specimens by immunofluorescence and immunoperoxidase staining.  (+info)

(7/1936) Effect of zinc on adenine nucleotide pools in relation to aflatoxin biosynthesis in Aspergillus parasiticus.

The adenylic acid systems of Aspergillus parasiticus were studied in zinc-replete and zinc-deficient media. The adenosine 5'-triphosphate levels of the fungus were high during exponential phase and low during stationary phase in zinc-replete cultures. On the other hand, the levels of adenosine 5'-diphosphate and adenosine 5'-monophosphate were low during exponential phase of growth and high during stationary phase. The adenosine 5'-triphosphate levels during exponential phase may indicate higher primary metabolic activity of the fungus. On the other hand, high adenosine 5'-monophosphate levels during stationary phase may inhibit lipid formation and may enhance aflatoxin levels. The inorganic phosphorus content was low in a zinc-replete medium throughout the growth period, thereby favoring aflatoxin biosynthesis. The energy charge during the exponential phase was high but low during the stationary phase. In general the energy charge values were lower because of high adenosine 5'-monophosphate content.  (+info)

(8/1936) Characterization of the promoter for the gene encoding the aflatoxin biosynthetic pathway regulatory protein AFLR.

Most genes in the aflatoxin biosynthetic pathway in Aspergillus parasiticus are regulated by the binuclear zinc cluster DNA-binding protein AFLR. The aflR promoter was analyzed in beta-glucuronidase reporter assays to elucidate some of the elements involved in the gene's transcription control. Truncation at 118 bp upstream of the translational start site increased promoter activity 5-fold, while truncation at -100 reduced activity about 20-fold. These findings indicate the presence of an important positive regulatory element between -100 and -118 and a negative regulatory region further upstream. Electrophoretic mobility shift assays on nuclear extracts from A. parasiticus induced for aflatoxin expression suggest that AFLR and another, possibly more abundant, protein bind to the -100/-118 region. Another protein binds to a sequence at position -159 to -164 that matches the consensus binding site for the transcription factor involved in pH-dependent gene regulation, PACC.  (+info)