Identification of a functional element in the promoter of the silkworm (Bombyx mori) fat body-specific gene Bmlp3.

30K proteins are a group of structurally related proteins that play important roles in the life cycle of the silkworm Bombyx mori and are largely synthesized and regulated in a time-dependent manner in the fat body. Little is known about the upstream regulatory elements associated with the genes encoding these proteins. In the present study, the promoter of Bmlp3, a fat body-specific gene encoding a 30K protein family member, was characterized by joining sequences containing the Bmlp3 promoter with various amounts of 5' upstream sequences to a luciferase reporter gene. The results indicated that the sequences from -150 to -250bp and -597 to -675bp upstream of the Bmlp3 transcription start site were necessary for high levels of luciferase activity. Further analysis showed that a 21-bp sequence located between -230 and -250 was specifically recognized by nuclear factors from silkworm fat bodies and BmE cells, and could enhance luciferase reporter-gene expression 2.8-fold in BmE cells. This study provides new insights into the Bmlp3 promoter and contributes to the further clarification of the function and developmental regulation of Bmlp3.