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A nuclear polyhedrosis virus (NPV) (Baculoviridae)-based gene expression system was improved by DNA recombination. The BmN cell line established from Bombyx mori and the Sf21 cell line established from Spodopterafrugiperda are non-permissive for Autographa californica multicapsid NPV (AcMNPV) and B. mori NPV (BmNPV) replication, respectively. After cotransfection of AcMNPV DNA and BamHI-digested BmNPV DNA into Sf21 cells, progeny viruses were isolated by plaque purification on BmN cell monolayers and the host specificity of one viral isolate was analysed. The virus had a wider host range, and replicated and produced polyhedra in Sf21 cells, BmN cells and larvae of the silkworm, B. morL DNA restriction endonuclease analysis showed that the isolate was a hybrid of AcMNPV and BmNPV. Using

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We investigate the structure and chemical composition of silk proteins produced by silkworms reared entirely on an artificial (A) diet, and compared those with worms entirely on a mulberry leaf ( M ) diet. The artificial diet has tofu-cake as its main component. Two types of cocoons (A and M) are used as sample materials. The dissolution behavior of the A sericin in hot water is different from that of M sericin; the amount of A sericin dissolved (28%) is higher than that of M (24%), and the dissolution rate of A sericin is also higher. Both sericins are separated into four fractions according to dissolution rate in hot water, and the amino acid composition (AAC) of each fraction is determined. Although the AAC of unfractionated A sericin is almost