Silk gland factor-1 involved in the regulation of Bombyx sericin-1 gene contains fork head motif.

Silk gland factor-1 (SGF-1) regulates transcription of the Bombyx sericin-1 gene via interaction with the SA site. In this study, two related SGF-1 polypeptides of apparent molecular masses of 40 and 41 kDa were purified. Specific interaction of these proteins with the SA site was demonstrated by electrophoretic mobility shift and dimethyl sulfate methylation interference assays. The SGF-1 40-kDa protein was partially sequenced and characterized as a new member of the fork head/HNF-3 family. Several full-length cDNAs encoding the SGF-1 40-kDa and possibly also the 41-kDa proteins were cloned and sequenced. SGF-1 mRNA is expressed consistently with the presumed role of the SGF-1 protein product in regulating the sericin-1 gene. The SGF-1 protein contains putative transactivation domains. We conclude that the 40- and 41-kDa SGF-1 proteins affect transcription of the sericin-1 gene via binding to the SA site.