Profiles of embryonic nuclear protein binding to the proximal promoter region of the soybean β‐conglycinin α subunit gene

β‐Conglycinin, a major component of seed storage protein in soybean, comprises three subunits: α, α′ and β. The expression of genes for these subunits is strictly controlled during embryogenesis. The proximal promoter region up to 245 bp upstream of the transcription start site of the α subunit gene sufficiently confers spatial and temporal control of transcription in embryos. Here, the binding profile of nuclear proteins in the proximal promoter region of the α subunit gene was analysed. DN ase I footprinting analysis indicated binding of proteins to the RY element and DNA regions including box I, a region conserved in cognate gene promoters. An electrophoretic mobility shift assay ( EMSA ) using different portions of box I as a probe revealed that multiple portions of box I bind to nuclear proteins. In addition, an EMSA using nuclear proteins extracted from embryos at different developmental stages indicated that the levels of major DNA –protein complexes on box I increased during embryo maturation. These results are consistent with the notion that box I is important for the transcriptional control of seed storage protein genes. Furthermore, the present data suggest that nuclear proteins bind to novel motifs in box I including 5′‐ TCAATT ‐3′ rather than to predicted cis ‐regulatory elements.