WC-1 is both a photoreceptor and a zinc-finger DNA-binding protein, whereas its partner, WC-2, contains transcriptional activation domains essential for the WCC to function properly ( He et al., 2002 Cheng et al., 2003 ). Light-signal transduction in Neurospora is mediated by the White Collar complex (WCC), a heterodimer of WC-1 ( Ballario et al., 1996, 1998 ) and WC-2 ( Linden and Macino, 1997), proteins that form a photoresponsive transcription factor complex ( Crosthwaite et al., 1997 Talora et al., 1999 Cheng et al., 2002 ). In Neurospora, one of the most important extracellular cues is light, and a proper response to this stimulus is crucial for its survival. During evolution various mechanisms have been selected to enable an organism to rapidly sense and respond to environmental light cues. Overall our data indicate that Neurospora and higher eukaryotes share a common mechanism for the signal transduction of environmental stimuli.Īll organisms need to respond to rapid changes in their environment. Finally, we provide evidence for a NGF-1–independent acetylated form of WC-1. Our data suggest that a WC-1/NGF-1 complex is preassembled in the dark on light-inducible promoters and that, after exposure to light stimulation, NGF-1–associated HAT activity leads to histone H3 acetylation and transcriptional activation. To support this view, we show a direct association between WC-1 and NGF-1 that depends on a WC-1 region containing a conserved functional LXXLL motif, a signature previously described as being an exclusive feature of NR/coactivator interaction. Here we describe a scenario in which WC-1 represents a functional orthologue of NRs and acts through association with the chromatin-modifying coactivator NGF-1, which encodes a homologue of the yeast Gcn5p acetyltransferase.
Its location in the nucleus and heterodimerization with WC-2, together with the presence of a zinc-finger DNA-binding domain and an environmental sensor domain, all resemble the functional evolutionary architecture adopted by vertebrate nuclear receptors (NRs). In addition to its transcriptional activity, WC-1 is able to directly sense light stimuli through a LOV sensor domain. In Neurospora crassa and other filamentous fungi, light-dependent–specific phenomena are regulated by transcription factors WC-1 and WC-2.
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