[Photoreceptor apparatus of a fungus Neurospora crassa].

Light governs living functions of ascomycete fungus Neurospora crassa by controlling expression of the genes responsible for differentiation of reproductive structures, synthesis of secondary metabolites and the circadian oscillator activity. Illumination also influences electrogenic processes in cell membrane and the activity and molecular organization of some enzymes. The major but, probably, not the sole photoreceptor pigment in Neurospora cells is WCC, a heterodimeric complex formed by PAS-domain-containing polypeptides WC-1 and WC-2, which are the products of genes white collar-1 and white collar-2. Mutation of any of these genes arrests most of the organism's responses to light. The photoreceptor belongs to a recently discovered vast group of non-homologous light-sensitive proteins, whose molecules bind flavin coenzymes as the photosensor chromophores. The photosignal transduction is started by excitation and photochemical activity of excited FAD molecule non-covalently bound by LOV-domain (a specialized version of PAS-domain) in WC-1 protein. The presence in both WC-1- and WC-2-proteins of "zinc fingers" (the GATA recognizing sequences) suggested that these motives might act as transcription factors. The critical analysis of photoinduction mechanism has shown, however, that promoters of light-sensitive genes do not contain a common cis-acting element, what makes to look for alternative mechanisms underlying photoregulated gene activity.