Transcription regulator that specifically up-regulates the gene cluster that mediates the biosynthesis of the isocyanide xanthocillin and its derivatives. Expressed during copper starvation via the regulation of both aceA and macA transcription factors. Virtually eliminates the production of all pathway metabolites, including fumiformamide, melanocin E, melanocin F, but also the sulfated xanthocillin derivative BU-4704 and xanthocillin X monomethyl ether. Belongs to the bZIP family.