May function as a transcription factor involved in light regulation. Binds and affects blue light regulation of the al-3 gene. Wc-1 and wc-2 proteins interact via homologous PAS domains, bind to promoters of light regulated genes such as frq, and activate transcription. Heterodimer of wc-1 and wc-2. By blue light. The glutamine-rich domain might function in activating gene expression. FMN binds covalently to cysteine after exposure to blue light and is reversed in the dark.