Structure and expression of gene coding for sex-specific storage protein of Bombyx mori

A major plasma protein termed "SP 1" accumulates in a sex- and stage-specific manner in the larval hemolymph of the silkworm, Bombyx mori. We have cloned the genomic sequence coding for SP 1 and analyzed its primary structure. The SP 1 mRNA sequence is encoded by five exons interspersed with four introns. Initiation site for the SP 1 gene transcription was identified at nucleotide level. Sequence homologous to the SV 40 enhancer "core" structure exists in two adjacent locations in the first intron. The 5' flanking region of the SP 1 gene contains a sequence highly homologous to the putative hormone-receptor complex binding site found in the ecdysteroid-sensitive genes of Drosophila melanogaster. Developmental change in the level of the SP 1 mRNA precursor in the fat body faithfully reflects that of SP 1 mRNA, indicating that the biosynthesis of SP 1 in B. mori is regulated in a sex- and stage-specific fashion at the level of transcription.