Timothy Fowler

REGULATION OF THE GLAA GENE OF ASPERGILLUS NIGER

SummaryThe glucoamylase gene of Aspergillus niger, glaA, is expressed at high levels in the presence of starch. We have determined the nucleotide sequence of 1966 bp of the 5′ flanking region of the glaA gene and have begun to identify sequences important for the control of glaA expression by deletion analysis. Constructs containing deletions extending into the glaA gene promotor were introduced into an A. niger host whose own glaA gene had been disrupted by a gene replacement event. Secreted levels of glucoamylase, expressed from each of the recombinant glaA genes, were measured by enzyme immunoassay. The effect of each deletion on the expression of glaA, when grown on differering carbon sources, was used to determine the limits of sequences upstream of glaA responsible for gene regulation. A region between -562 and -318 appears to direct high-level expression, whereas only 214 bp of 5′ flanking sequence is required to initiate the start to transcription.

The catR gene encoding a catalase from Aspergillus niger : primary structure and elevated expression through increased gene copy number and use of a strong promoter

Synthetic oligonucleotide probes based on amino acid sequence data were used to identify and clone cDNA sequences encoding a catalase (catalase‐R) of Aspergillus niger. One cDNA clone was subsequently used to isolate the corresponding genomic DNA sequences (designated catR). Nucleotide sequence analysis of both genomic and cDNA clones suggested that the catR coding region consists of five exons interrupted by four small introns. The deduced amino acid sequence of catalase‐R spans 730 residues which show significant homology to both prokaryotic and eukaryotic catalases, particularly in regions involved in catalytic activity and binding of the haem prosthetic group. Increased expression of the catR gene was obtained by transformation of an A. niger host strain with an integrative vector carrying the cloned genomic DNA segment. Several of these transformants produced three‐ to fivefold higher levels of catalase than the untransformed parent strain. Hybridization analyses indicated that these strains contained multiple copies of catR integrated into the genome. A second expression vector was constructed in which the catR coding region was functionally joined to the promoter and terminator elements of the A. niger glucoamylase (glaA) gene. A. niger transformants containing this vector produced from three‐ to 10‐fold higher levels of catalase‐R than the untransformed parent strain.

Secretion of Trichoderma reesei β-glucosidase by Saccharomyces cerevisiae

Abstract  An intronless form of the bgl1 gene encoding an extracellular β-glucosidase from Trichoderma reesei was expressed in the yeast Saccharomyces cerevisiae under the control of the yeast GAL1 promoter. Transformation of a yeast strain with this vector resulted in transformants that produce and secrete active β-glucosidase into the growth medium. Additionally, active recombinant β-glucosidase protein was shown to be localized predominantly in the periplasmic space by using a p-nitrophenyl β-D-glycoside hydrolysis assay against fractionated yeast cells. The apparent size of the recombinant enzyme was 10–15 kDa larger than that of the native form. Treatment of the recombinant β-glucosidase with endoglycosidase-H indicated the apparent increase in size was due to N-linked glycosylation.

Gene expression systems for filamentous fungi.

The extraordinary capacity of filamentous fungi to produce large quantities of extracellular protein, together with the advent of DNA-mediated fungal transformation, has resulted in rapid advances in the development of gene expression systems for filamentous fungi. This review focuses on recent developments in the expression of both fungal and non-fungal genes and improvements to the host.

Secretion ofTrichoderma reeseiβ-glucosidase bySaccharomyces cerevisiae

An intronless form of thebgl1 gene encoding an extracellularβ-glucosidase fromTrichoderma reesei was expressed in the yeast Saccharomyces cerevisiae under the control of the yeast GAL 1 promoter. Transformation of a yeast strain with this vector resulted in transformants that produce and secrete activeβ-glucosidase into the growth medium. Additionally, active recombinantβ-glucosidase protein was shown to be localized predominantly in the periplasmic space by using ap-nitrophenylβ-D-glycoside hydrolysis assay against fractionated yeast cells. The apparent size of the recombinant enzyme was 10–15 kDa larger than that of the native form. Treatment of the recombinantβ-glucosidase with endoglycosidase-H indicated the apparent increase in size was due to N-linked glycosylation.