The fibroin genes of Antheraea yamamai and Bombyx mori are different in their core regions but reveal a striking sequence similarity in their 5′ ends and 5′flanking regions

Abstract

We have cloned a fibroin gene from the Japanese oak silkworm, Antheraea yamamai, which belongs to the Saturniidae. The cloned DNA covers the entire region of the fibroin gene and a 1.4 kb 5′flanking sequence. Structural analysis of the gene by restriction mapping, S1 digestion and primer extension experiments shows that of Bombyx mori; both genes consist of one intron near the 5′end and two exons. Sequence comparison between the two genes reveals that the first exon of about 70 bp and the sequence around the splicing junctions, is very well conserved between the two species, whereas there is no sequence homology in the core region encoding the main polypeptide sequence. Interestingly, the 5′flanking sequence of the A. yamamai fibroin gene at -300 to -20 is homologous with that of B. mori in many patches including the TATA box region. Furthermore, the Antheraea fibroin gene could be transcribed faithfully in a posterior silk gland extract from B. mori. From this evidence, we conclude that the DNA sequence and the mechanisms that are necessary for fibroin gene expression in the posterior silk gland cells are probably conserved in the two families, Bombyx and Antheraea.