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  • 1
    ISSN: 1617-4623
    Keywords: Wild silkworm ; Fibroin gene ; 5′-end region ; Sequence comparison ; Domesticated silkworm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The fibroin gene of the wild silkworm Bombyx mandarina was identified through hybridization with the fibroin DNA of the domesticated species, B. mori. Using their cross homology, we isolated the clone carrying the fibroin gene from a B. mandarina genomic library in λ Charon 30. A resultant recombinant phage contained the DNA fragment corresponding to the 5′-end region of the B. mori fibroin gene. After subcloning the DNA fragment into pUC12, its DNA sequence was partially determined. Comparison of the nucleotide sequence of the 5′-end region from the two species showed that the B. mandarina fibroin gene is highly homologous to that of B. mori but the extent of homology varies in different functional domains within this region. In particular, the promoters and enhancer-like element sequences are identical in the two species, indicating that these regions are essential for fibroin gene expression irrespective of species. In contrast, there is an appreciable amount of base change in the region far upstream from the enhancer-like element sequence and in the intron-region. These results support the view that the B. mandarina which exists in nature at present is a possible ancestor of the domesticated silkworm, B. mori.
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  • 2
    ISSN: 1617-4623
    Keywords: Antheraea ; Bombyx ; Fibroin gene ; Sequence comparison ; In vitro transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 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.
    Type of Medium: Electronic Resource
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