In monkey COS cells only the TATA box and the cap site region are required for faithful and efficient initiation of the fibroin gene transcription.

The DNA sequences necessary for faithful and efficient initiation of transcription of Bombyx mori fibroin gene have been studied in vivo using monkey COS cells and a SV40 origin vector. Transcriptional analysis of 5' deletion genes and of exact substitution genes including a series of single base substitution mutants indicates that the TATA box and the cap region are required for faithful and efficient initiation of the fibroin gene transcription in vivo, whereas far upstream sequences and the CAAT-like sequences are not required. In addition, single base substitution genes of the cap site region have clearly shown that there exists a strict sequence requirement of the cap region of the fibroin gene. These results define the basic promoter of the fibroin gene to the region spanning the TATA box and the cap site region.