Transcription of a lepidopteran cytochrome P450 promoter is modulated by multiple elements in its 5′ UTR and repressed by 20-hydroxyecdysone

The biochemical response to the phytochemical xanthotoxin encountered in the diet of black swallowtail larvae is the induction of P450s capable of detoxifying this and other toxic furanocoumarins. As the xenobiotic response element to xanthotoxin (XRE-xan) is necessary but not sufficient for transcription of the CYP6B1v3 gene in Sf9 cells, sequences upstream of it, such as a putative EcRE, and downstream of it, such as a putative CIEBP binding site and lnr, have been tested for their roles in regulation. Mutation of the putative EcRE has indicated that it affects basal transcription of this promoter but not repression by 20-hydroxyecdysone. Mutation of the more proximal promoter sequence, including the CIEBP and lnr, have indicated that many core promoter elements between the TATA box and translation start site modulate basal and xanthotoxin-inducible expression of this composite promoter.