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Appl. Environ. Microbiol., 03 1996, 1036-1044, Vol 62, No. 3
DC la Grange, IS Pretorius and WH van Zyl
The XYN2 gene encoding the main Trichoderma reesei QM 6a endo-beta-1,4-
xylanase was amplified by PCR from first-strand cDNA synthesized on mRNA
isolated from the fungus. The nucleotide sequence of the cDNA fragment was
verified to contain a 699-bp open reading frame that encodes a
223-amino-acid propeptide. The XYN2 gene, located on URA3- based multicopy
shuttle vectors, was successfully expressed in the yeast Saccharomyces
cerevisiae under the control of the alcohol dehydrogenase II (ADH2) and
phosphoglycerate kinase (PGK1) gene promoters and terminators,
respectively. The 33-amino-acid leader peptide of the Xyn2 beta-xylanase
was recognized and cleaved at the Kex2-like Lys-Arg residues, enabling the
efficient secretion and glycosylation of the heterologous beta-xylanase.
The molecular mass of the recombinant beta-xylanase was estimated by sodium
dodecyl sulfate- polyacrylamide gel electrophoresis to be 27 kDa. The
construction of fur1 ura3 S. cerevisiae strains allowed for the
autoselection of the URA3-based XYN2 shuttle vectors in nonselective
complex medium. These autoselective S. cerevisiae strains produced 1,200
and 160 nkat of beta- xylanase activity per ml under the control of the
ADH2 and PGK1 promoters in rich medium, respectively. The recombinant
enzyme showed highest activity at pH 6 and 60 degrees C and retained more
than 90% of its activity after 60 min at 50 degrees C.
Copyright © 1996, American Society for Microbiology
Expression of a Trichoderma reesei beta-xylanase gene (XYN2) in Saccharomyces cerevisiae
Department of Microbiology, University of Stellenbosch, South Africa.
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