Transcription activation mediated by the bZIP factor SPA on the endosperm box is modulated by ESBF-1 in vitro

A modified in vitro transcription system has been used to study the functio n of the cloned bZIP transcription factor SPA and the binding activity ESBF I in activating transcription from the bifactorial endosperm box region of the wheat prolamin LMWG-1D1 gene. Recombinant SPA expressed in Escherichia coli activated transcription from the endosperm box motif, and this was de pendent upon the binding of the nuclear protein ESBF I. ESBF I did not acti vate transcription independently, but potentiated SPA-mediated transcriptio nal activation. ESBF I is likely to be the equivalent of, or contain the re cently characterised DOF class of, Zn-finger protein called WPBF. These dat a provide new information about the interplay of members of the bZIP and DO F transcription factor families in regulating expression from bifactorial s ites found in a variety of plant promoters.