Candida Infection Biology – fungal armoury, battlefields ... - FINSysB

Poster number: 15
Target specificity of the Efg1 regulator in Candida albicans
Lassak, T., Lagadec, Q., Kurtz, D., Bussmann, M. and Ernst, J. F.
Heinrich-Heine-Universität Düsseldorf, Institut für Mikrobiologie, Molekulare Mykologie
Efg1 is a general transcription factor, which regulates numerous morphogenetic
and metabolic processes in C. albicans. We previously found that overexpression
of EFG1 and activation of Efg1 during hypha formation leads to downregulation of
EFG1 promoter activity and that EFG1 downregulation is necessary to allow the
formation of true hyphae and prevent pseudohyphal growth.
To explore the Efg1 binding specificity its binding to the EFG1 promoter was
analyzed by EMSA and footprint analyses. These experiments revealed binding of
Efg1 to a promoter sequence close to the transcript start site, which contained a
repeated 8-mer motif (referred to as APSES response element, ARE). Surprisingly,
promoter fusions to the RLUC reporter lacking the ARE motif were still able to
downregulate the EFG1 promoter during hypha formation in an Efg1-dependent
manner. Furthermore, extensive deletions of the 10 kb-large 5 untranslated region
of EFG1 still did not prevent regulation suggesting multiple binding sites for Efg1
within the EFG1 promoter. We subsequently analyzed genome-wide occupation of
chromosomal sequences by Efg1 using ChIP chip analysis. These results revealed
the entire 10 kb EFG1 upstream region as a major site of Efg1 occupancy.
Unexpectedly, Efg1 binding to this region was rapidly lost during hypha induction
suggesting a regulatory model, in which Efg1 acts as transcriptional activator
specifically during yeast growth. In further experiments we attempted to reconstitute
the EFG1 autoregulatory circuit in the yeast S. cerevisiae. In this system the
presence of Efg1 was shown to downregulate EFG1 promoter activity, although
not to the same extent as was observed in C. albicans. This finding hints at
co-regulators that together with Efg1 mediate autoregulation in C. albicans.
We are grateful to the European Commission for funding the FINSysB Marie Curie Initial Training Network
(PITN-GA-2008-214004).
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