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Hap4p overexpression in glucose-grown Saccharomyces cerevisiae induces cells to enter a novel metabolic state

Romeo Lascaris13*, Harmen J Bussemaker14, André Boorsma1, Matt Piper2, Hans van der Spek1, Les Grivell15 and Jolanda Blom1

Author Affiliations

1 Swammerdam Institute for Life Sciences, University of Amsterdam, 1098 SM Amsterdam, The Netherlands

2 Kluyver Laboratory of Biotechnology, TU Delft, Julianalaan 67, 2628 BC Delft, The Netherlands

3 Current address: Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands

4 Current address: Department of Biological Sciences and Columbia Genome Center, Columbia University, 1212 Amsterdam Avenue MC 2441, New York, NY 10027, USA

5 Current address: EMBO, Meyerhofstrasse 1, D-69117 Heidelberg, Germany

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Genome Biology 2002, 4:R3  doi:10.1186/gb-2002-4-1-r3

Published: 17 December 2002



Metabolic and regulatory gene networks generally tend to be stable. However, we have recently shown that overexpression of the transcriptional activator Hap4p in yeast causes cells to move to a state characterized by increased respiratory activity. To understand why overexpression of HAP4 is able to override the signals that normally result in glucose repression of mitochondrial function, we analyzed in detail the changes that occur in these cells.


Whole-genome expression profiling and fingerprinting of the regulatory activity network show that HAP4 overexpression provokes changes that also occur during the diauxic shift. Overexpression of HAP4, however, primarily acts on mitochondrial function and biogenesis. In fact, a number of nuclear genes encoding mitochondrial proteins are induced to a greater extent than in cells that have passed through a normal diauxic shift: in addition to genes required for mitochondrial energy conservation they include genes encoding mitochondrial ribosomal proteins.


We show that overproduction of a single nuclear transcription factor enables cells to move to a novel state that displays features typical of, but clearly not identical to, other derepressed states.