Multiple nuclear factors interact with upstream sequences of differentially regulated β-conglycinin genes

The expression of the α′ and β subunit genes of β-conglycinin is differentially regulated during soybean embryo development. Although both are expressed solely in developing seeds during mid to late stages of embryo development, the α′ subunit is expressed more highly on a per gene basis, and α′ subunit mRNA begins to accumulate three to five days earlier than β subunit mRNA. In cultured cotyledons, β subunit genes respond to changes in methionine or abscisic acid levels, whereas expression of the α′ subunit gene(s) is unaffected by these changes. To investigate the mechanisms by which these genes are transcriptionally regulated, we examined the interactions of nuclear proteins with upstream sequences from the α′ and β subunit genes. Four distinct DNA binding factors were identified in nuclear extracts from developing soybean seeds. These factors are termed Soybean Embryo Factors (SEF) 1 through 4. SEF binding sites are distributed non-uniformly between the α′ and β subunit genes, and the amount of protein binding is modulated over the course of embryo development. DNA footprinting revealed the sequences recognized by three of these factors. Factors which behave in a manner similar to that of SEF3 were also identified in nuclear extracts from developing tobacco and sunflower seeds.