This paper describes cDNAs of four small-size proteins that occur in the cocoon silk of Bombyxmori. Two of them (9.9 and 10.3 kDa), which have the N-terminal sequences and the spacing of a few amino acids at C-termini similar to the seroin of Galleria mellonella, are called seroin 1 and seroin 2. The corresponding genes are expressed in the middle, and to a small extent also in the posterior silk gland sections. The seroin 1 and less conspicuously the seroin 2 mRNAs accumulate in the course of the last larval instar to a maximum in postspinning larvae. Two other proteins (6 kDa and 4.7 kDa) of B. mori cocoons were identified as a typical Kunitz-type and a somewhat unusual Kazal-type proteinase inhibitors, and named BmSPI 1 and BmSPI 2, respectively. Their genes are expressed in the middle, and the BmSPI 1 gene slightly also in the posterior silk gland sections. The expression ensues a few days after the last larval ecdysis and increases until the cocoon spinning. Post-spinning larvae still contain high amounts of the BmSPI 1 but no BmSPI 2 transcripts. It is assumed that seroins and proteinase inhibitors are involved in cocoon protection against predators and microbes.

Institute of Entomology Academy of Sciences and Faculty of Biological Sciences University of South Bohemia Ceské Budejovice Czech Republic

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Modular structure, sequence diversification and appropriate nomenclature of seroins produced in the silk glands of Lepidoptera

Silks produced by insect labial glands

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AF352583, AF352584, AF352585, AF354456