Roles in dimerization and blue light photoresponse of the PAS and LOV domains of Neurospora crassa white collar proteins

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Abstract
The genes coding for white collar‐1 and white collar‐2 (wc‐1 and wc‐2 ) have been isolated previously, and their products characterized as Zn‐finger transcription factors involved in the control of blue light‐induced genes. Here, we show that the PAS dimerization domains present in both proteins enable the WC‐1 and WC‐2 proteins to dimerize in vitro. Homodimers and heterodimers are formed between the white collar (WC) proteins. A computer analysis of WC‐1 reveals a second domain, called LOV, also identified in NPH1, a putative blue light photoreceptor in plants and conserved in redox‐sensitive proteins and in the phytochromes. The WC‐1 LOV domain does not dimerize with canonical PAS domains, but it is able to self‐dimerize. The isolation of three blind wc‐1 strains, each with a single amino acid substitution only in the LOV domain, reveals that this region is essential for blue light responses in Neurospora. The demonstration that the WC‐1 proteins in these LOV mutants are still able to self‐dimerize suggests that this domain plays an additional role, essential in blue light signal transduction.