Role of the Core Promoter for the Preferential Transcription of Fibroin Gene in the Posterior Silk Gland Extract

Preferential transcription of the fibroin gene in homologous cell-free transcription systems prepared from the posterior silk gland (psg) of Bombyx mori is supported by the modulators upstream and downstream of the core promoter. However, we found that the cognate fibroin core promoter composed of the TATA box and transcription initiation region was indispensable for this preferential transcription in the psg extract. Studies on the transcriptional efficiencies of reconstituted fibroin promoters indicated that the fibroin core promoter functions synergistically with the modulators. The core promoter of adenovirus major late promoter (AdMLP) which carries the same TATA box sequence as the fibroin promoter could not substitute for the fibroin core promoter for the preferential transcription. In DNase I footprint experiments a characteristic protection pattern was obtained on the fibroin core promoter specifically in the psg extract but not in the HeLa cell extract, and the pattern on the fibroin core promoter was distinguished from that on AdMLP. Appearance of the characteristic footprint pattern on the core promoter and promoter activity of the fibroin gene were correlated in the psg extract. These results suggest that specific interaction of the transcription machinery with fibroin core promoter in the psg extract is a basis of psg specific transcription of the fibroin gene.