Sequence polymorphisms in the 5′-upstream region of the fibroin H-chain gene in the silkworm, Bombyx mori

DNA fragments containing the fibroin H-chain gene from two different strains Bombys mori, J-139 and Nd (2) were cloned into phage λ charon 4A. Comparison of the restriction sites in these cloned DNAs revealed that in addition to the known polymorphism in the region coding for the repetitive amino acid sequence of the fibroin H-chain [Manning and Gage, J. Biol. Chem. 255 (1980) 9451-9457], at least two other types of polymorphism were present, one around the 5′ end of the structural gene, and the other in the far upstream region of the gene. Restriction sites around the 5′ end of the gene were well conserved between these strains, but some heterogeneity, suggesting the presence of small insertions, deletions or base changes, was noted. In contrast, DNA sequences of the region 2-4 kb upstream from the 5′ end of the gene were markedly different between these two strains, indicating that either a deletion or an insertion of a DNA sequence longer than 2 kb had occurred in this region. Comparison with several other strains suggested that the observed changes in the far-upstream region were unique to the Nd(2) strain.