The complete nucleotide sequence of the Eri-silkworm (Samia cynthia ricini) fibroin gene

抄録

We examined 8,640 bp of the Samia cynthia ricini (Scr) fibroin gene together with the 5’ and 3’ flanking sequences and deduced the Scr-fibroin amino acid sequence. A large region of the Scr-fibroin amino acid sequence consists of repetitive arrays, which include a common polyalanine block and one of four variable nonpolyalanine blocks. These four types of nonpolyalanine blocks were rich in glycine (Gly) residues, differing from saturniid fibroins in which at least one type of nonpolyalanine block is Gly poor. The presence of abundant Gly residues increases the GC content of the Scr-fibroin gene. However, preferential use of GGA and GGU isocodons for Gly decreases the GC content. The amino acid sequences of C-terminal regions among saturniid fibroins were conserved, but were considerably diversified from non-saturniid fibroins. Three conserved Cys residues in the C-terminal region, which are conserved in Antheraea pernyi and A. yamamai fibroins, contribute to S-S bond formation between the fibroin homodimers, although another three cysteine residues conserved between C-terminal regions of Bombyx mori and Galleria mellonella fibroin heavy chain contribute to formation of disulfide bonds between fibroin heavy chain (fhc) and fibroin light chain (flc).