ROLES IN DIMERIZATION AND BLUE-LIGHT PHOTORESPONSE OF THE PAS AND LOVDOMAINS OF NEUROSPORA-CRASSA WHITE-COLLAR PROTEINS

The genes coding for white collar-1 and white collar-2 (wc-1 and we-2) have been isolated previously, and their products characterized as Zn -finger transcription factors involved in the control of blue light-in duced genes, Here, we show that the PAS dimerization domains present i n 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 phytochrom es, 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 str ains, each with a single amino acid substitution only in the LOV domai n, reveals that this region is essential for blue light responses in N eurospora, The demonstration that the WC-1 proteins in these LOV mutan ts are still able to self-dimerize suggests that this domain plays an additional role, essential in blue light signal transduction.