HISTONE H1 ENHANCES THE DNA-BINDING ACTIVITY OF THE TRANSCRIPTION FACTOR EMBP-1

Previous work indicated that nuclear extracts isolated from embryogeni c rice suspension cells treated with the phytohormone abscisic acid (A BA) have enhanced binding activity to an ABA response element (Emla) i n the promoter of the Em gene from wheat, We identified an activity in wheat and maize nuclear extracts that enhances binding of the recombi nant transcription factor EmBP-1 to Emla by 80-fold. Fractionation of nuclear extracts led us to identify histone H1 and HMGb (but not HMGc or -d) as two factors that can enhance the ability of EmBP-1 to bind t o Emla and account for at least a part of this activity of nuclear ext racts. Our results, which indicate for the first time that histone ill possesses this type of activity, lend further support to the model th at positively charged proteins can drastically affect the DNA binding activity of specific transcription factors. Furthermore, our study poi nts to these chromosomal proteins as potential targets of an ABA-media ted modification (e.g. acetylation) that could affect the regulation o f Em gene expression.