A contribution of the core-promoter and its surrounding regions to the preferential transcription of the fibroin gene in posterior silk gland extracts.

Complementation of a posterior silk gland (psg) extract to a HeLa cell extract specifically enhances the transcription of the Bombyx mori fibroin gene. To map the regions responsible for this enhancement, the fibroin promoter was dissected and the transcriptional function of each region was analyzed. Besides the upstream promoter element 5' to the TATA box, two downstream elements were found to be important for the preferential transcription of the fibroin gene in the complementation system as well as in the psg extract. The minimal fibroin promoter from -37 to +10 (core-promoter) was preferentially transcribed in the psg extract, while the transcription efficiencies of other promoters like one of the Bombyx chorion genes and the adenovirus 2 major late promoter (Ad2MLP) were considerably lower. The transcription from the core-promoter was further enhanced when combined with either the intronic element from +156 to +454 or the upstream element. Both the upstream and intronic elements also stimulated the transcription from the Ad2MLP in an orientation independent manner. These results demonstrate that the transcription of the fibroin gene is mediated through an integration of multiple regulatory elements.