Major ampullate silk, also known as dragline silk, from spiders is one of the strongest biomaterials known. The major ampullate spidroin 1 (MaSp1) of the Japanese golden orb-web spider, Nephila clavata, has never been characterized. Here we report the sequence of the C-terminal region of MaSp1 from N. clavata. We have cloned a partial cDNA of 905 bp length encoding MaSp1. The deduced amino acid sequence from the partial cDNA contained the repetitive sequence of 165 amino acids and the non-repetitive sequence of 99 amino acids toward the C-terminus. This repetitive sequence consisted of three amino acid motifs, An, (GA)n and GGX. This repetitive region had an amino acid composition similar to the crystalline region of Bombyx mori fibroin H with two differences: low Ser content and high Gln content in MaSp1. In contrast to the crystalline region of fibroin H that is present in hydrophobic parts, the repetitive region of MaSp1 shows an oscillating pattern of hydrophobic and hydrophilic parts. The N. clavata dragline silk had an ultimate tensile strength (UTS) of 1300MPa. The UTS obtained in the N. clavata dragline silk is significantly higher than that in the silkworm silk. The quality of Bombyx silk would be improved by replacing fibroin H with MaSp1 or by making a mixture of fibroin H and MaSp1 in the transgenic silkworm that spin spider silk.
The lifespan of the imago in the silkworm, Bombyx mori, is around one week. The N251 strain maintained at the Tokyo University of Agriculture and Technology has the short lifespan for imagoes dying within 4 days. It was clear from the mating experiment that the characteristic of this short lifespan is controlled by a single recessive gene. Linkage analysis of the gene regarding “Short lifespan in imago (symbol sli)” was performed by Hara's scanning linkage analysis method. The sli gene is linked with the twenty-first cDNA linkage group and three-point experiments involving m268, m497 and sli revealed that the sli gene was located between m268 and m497. The locus of the sli gene has been determined with correction to be 7.2cM from m268 at the position 0.0 on the restriction fragment linkage group 21 (RFLG21).