Transcription activator that specifically regulates the expression of the gene cluster that mediates the biosynthesis of calbistrins and related compounds such as decumbenones. Calbistrin A is a secondary metabolite with an interesting structure that was recently found to have bioactivity against leukemia cells. It consists of two polyketides linked by an ester bond: a bicyclic decalin containing polyketide and a linear 12 carbon dioic acid structure. Expression is induced in complex medium (Czapek yeast autolysate medium) supporting calbistrin production. Abolishes the production of calbistrin and of the related metabolites decumbenones, whereas production of unrelated compounds, such as andrastin C, remains unaffected (PubMed:30598828). Results in a significant down-regulation of the expression of the calbistrin biosynthesis cluster genes calA, calB and calF (PubMed:30598828). Calbistrin A has been reported to possess a number of interesting bioactivities including antifungal active against Candida albicans and cytotoxic toward both healthy and leukemic human cells.