A CONSERVED DOMAIN OF THE VIVIPAROUS-1 GENE-PRODUCT ENHANCES THE DNA-BINDING ACTIVITY OF THE BZIP PROTEIN EMBP-1 AND OTHER TRANSCRIPTION FACTORS

The maize VP1 protein is a seed-specific regulator of gene expression that effects the expression of a subset of abscisic acid (ABA)-regulat ed genes that are expressed during the maturation program of the seed. In addition, VP1 has pleiotropic effects on seed development that are not related to ABA. In transient expression assays, VP1 has been show n to transactivate gene expression through at least two distinct promo ter elements: the G boxes from the ABA-inducible wheat Em gene and the SphI box from the maize C1 gene. We have investigated how VP1 can tra nsactivate gene expression through diverse promoter elements by analyz ing its association in vitro with EmBP-1, a factor that binds the Em p romoter. We demonstrate that VP1 can greatly enhance the DNA binding a ctivity of EmBP-1 in a gel retardation assay. This enhancing activity has also been observed on transcription factors as diverse as Opaque-2 , Max, Sp1, and NF-kappa B. Deletion of a small but highly conserved r egion (BR2) in VP1 eliminates the enhancement in vitro as well as the ability of VP1 to transactivate Em gene expression in a transient expr ession assay. A 40-amino acid fragment from VP1 sandwiched between the maltose-binding protein and LacZ can confer the enhancement function to this fusion protein in vitro. A weak and relatively nonspecific int eraction between BR2 and DNA is demonstrated by UV cross-linking. The in vitro properties we observe for VP1 might explain the regulatory ef fects of VP1 on a diverse set of genes and why mutations in the vp1 lo cus have pleiotropic effects.