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Eukaryotic Cell doi:10.1128/EC.00033-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Functional mapping of the Candida albicans Efg1 regulator

Institut für Mikrobiologie, Molekulare Mykologie, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany

^* To whom correspondence should be addressed. Email: joachim.ernst{at}uni-duesseldorf.de.

	Abstract

Efg1p is a key transcriptional regulator in Candida albicans, which controls various aspects of morphogenesis and metabolism in this organism. Efg1p contains a central bHLH domain, flanked by sequences highly conserved in fungal APSES proteins, as well as polyglutamine stretches at the N- and C-terminal ends. A systematic deletion approach to specify functional domains of Efg1p revealed that the APSES domain is essential for morphogenesis of the normal yeast and true hyphal cell forms and that bHLH flanking sequences are needed for Efg1p stability. Additional C-terminal sequences were required for hypha formation on some inducing media and most of Efg1p sequences were needed for chlamydospore morphogenesis. Overexpression of EFG1 led to pseudohypha formation only if a functional APSES domain was present, while a switch from the opaque to white cell type in addition depended on the presence of certain N- and C-terminal segments. Yeast hybrid experiments revealed that binding of Efg1p to its antagonist Czf1p required two regions outside of the APSES domain, which did not coincide with Efg1p-sequences needed for its transcriptional repressor activity. Binding of the Flo8 transcription factor to Efg1p did not require the APSES domain but appeared to occur at two or more redundant domains. In contrast, DNA binding of Efg1p to a MCB element solely required the APSES domain. Overall, these results suggest that functional domains of Efg1p are spread throughout most of its sequences, including the central APSES domain involved in DNA-binding, as well as flanking regions required for various protein interactions and regulatory activities.