Browsing by Author "Navarro, C"

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    Differences in expression of two endoxylanase genes (xynA and xynB) from Penicillium purpurogenum
    (2002) Chávez, R; Schachter, K; Navarro, C; Peirano, A; Aguirre, C; Bull, P; Eyzaguirre, J
    A number of xylanolytic microorganisms secrete to the medium several molecular forms of endoxylanases. The physiological function of these isoforms is not clears one possibility is that they are produced under different growth conditions. To study this problem, we have used two endoxylanases (XynA and XynB) produced by the fungus Penicillium purpurogenum. These enzymes have been previously purified and characterized; they belong to family 10 and 11 of the glycosyl hydrolases, respectively. The promoters of the xynA and xynB genes have been sequenced: both present consensus sequences for the binding of the carbon catabolite repressor CreA, but otherwise show substantial differences. The xynB promoter has eight boxes in tandem for the binding of the XlnR activator and lacks the consensus sequence for the PacC pH regulator. On the other hand, the xynA promoter contains one XlnR box and three PacC consensus sequences. To investigate if these differences are reflected in gene expression, Northern blot assays were carried out. The xynA gene is transiently expressed when oat spell xylan is used as carbon source, but negligible expression was observed with birchwood xylan, xylose or xylitol. In contrast, xynB is broadly induced by all these carbon sources; this may be related to the presence of several XlnR boxes. Similar results were obtained by zymogram analysis of the expressed proteins. The different induction capabilities of birchwood and oat spelt xylan may be due to differences in their composition and structure. Expression assays carried out at different pH reflects that, despite the lack of PacC binding sites in the xynB promoter, this gene is tightly regulated by pH. The findings described here illustrate new and important differences between endoxylanases from families 10 and 11 in P. purpurogenum. They may help explain the production of multiple endoxylanase forms by this organism. (C) 2002 Published by Elsevier Science B.V.
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    Secretion of endoxylanase A from Penicillium purpurogenum by Saccharomyces cerevisiae transformed with genomic fungal DNA
    (2002) Chávez, R; Navarro, C; Calderón, I; Peirano, A; Bull, P; Eyzaguirre, J
    Saccharomyces cerevisiae was transformed with a genomic library from Penicillium purpurogenum, and an endoxylanase-producing yeast clone (named 44A) that grows on xylose or xylan as sole carbon source was isolated. This yeast synthesizes xynA mRNA and secretes endoxylanase A to culture media when grown on xylan or xylose, but not glucose. Analysis by pulse-field gel electrophoresis and sequencing indicates that xynA, including its eight introns, has been inserted into the yeast genome. It was shown by sequencing that clone 44A is able to correctly splice xynA introns. This is the first successful attempt to express a fungal endoxylanase gene in yeast with correct intron splicing. (C) 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
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    The acetyl xylan esterase II gene from Penicillium purpurogenum is differentially expressed in several carbon sources, and tightly regulated by pH
    (2004) Chávez, R; Schachter, K; Navarro, C; Peirano, A; Bull, P; Eyzaguirre, J
    The expression of the acetyl xylan esterase II (axell) gene from Penicillium purpurogenum is repressed by glucose and induced by xylan, as well as to a small degree by xylose and xylitol. This gene is expressed at neutral pH, but not tinder alkaline or acidic conditions, in agreement with previous findings for other xylanolytic genes of this organism. This is the first report showing pH regulation of an axe gene.