Résumé
To identify the functional regulatory elements of the promoter of the cytoplasmic actin
A3 gene in
Bombyx mori, transient expression of A3-LacZ mutants was assayed in cultured
Lepidoptera cells. This led to the recognition of two proximal and contiguous domains exerting strong negative and positive effects, respectively on promoter activity. The negative region contains a ten-base-pair sequence that binds
Bombyx silk gland cell nuclear proteins
in vitro. The positive regulatory element was identified as a serum response element (SRE) by its sequence, and its
in vitro binding properties. Moreover, structural analysis of posterior and median silk gland cell chromatin by dimethyl sulfate-aided LMPCR revealed that SRE is bound to its cognate factor
in situ, in most, if not all, the ∼100,000
A3 copies of the polyploid DNA stock. The regulation of the
A3 promoter in the silk gland would thus result from the combined action of these two antagonist factors.