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J. Biol. Chem., Vol. 282, Issue 25, 18654-18659, June 22, 2007

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Induction of the gal Pathway and Cellulase Genes Involves No Transcriptional Inducer Function of the Galactokinase in Hypocrea jecorina^*

From the Molecular Biotechnology Group, Research Area Gene Technology and Applied Biochemistry, Institute of Chemical Engineering, Technische Universität Wien, Getreidemarkt 9-166.5, A-1060 Vienna, Austria

The Saccharomyces cerevisiae galactokinase ScGal1, a key enzyme for D-galactose metabolism, catalyzes the conversion of D-galactose to D-galactose 1-phosphate, whereas its catalytically inactive paralogue, ScGal3, activates the transcription of the GAL pathway genes. In Kluyveromyces lactis the transcriptional inducer function and the galactokinase activity are encoded by a single bifunctional KlGal1. Here, we investigated the cellular function of the single galactokinase GAL1 in the multicellular ascomycete Hypocrea jecorina (= Trichoderma reesei) in the induction of the gal genes and of the galactokinase-dependent induction of the cellulase genes by lactose (1,4-O--D-galactopyranosyl-D-glucose). A comparison of the transcriptional response of a strain deleted in the gal1 gene (no putative transcriptional inducer and no galactokinase activity), a strain expressing a catalytically inactive GAL1 version (no galactokinase activity but a putative inducer function), and a strain expressing the Escherichia coli galK (no putative transcriptional inducer but galactokinase activity) showed that, in contrast to the two yeasts, both the GAL1 protein and the galactokinase activity are fully dispensable for induction of the Leloir pathway gene gal7 by D-galactose and that only the galactokinase activity is required for cellulase induction by lactose. The data document a fundamental difference in the mechanisms by which yeasts and multicellular fungi respond to the presence of D-galactose, showing that the Gal1/Gal3-Gal4-Gal80-dependent regulatory circuit does not operate in multicellular fungi.

Received for publication, February 1, 2007 , and in revised form, April 4, 2007.

^* This work was supported by Grant P16143 [GenBank] from the Austrian Science Foundation and Grant QLK3-1999-00729 from the Fifth EC Framework Program (Quality of Life and Management of Living Resources, Project EUROFUNG 2) (to C. P. K.) and by the Scientific and Technological Co-operation Program of the Austrian Exchange Service (25/2005) (to B. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed. Tel.: 43-1-58801-17210; Fax: 43-1-58801-17299; Web site: www.vt.tuwien.ac.at; E-mail: lhartl{at}mail.zserv.tuwien.ac.at.

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