CONSTITUTIVE AND CELL-DIVISION-INDUCIBLE PROTEIN-DNA INTERACTIONS IN 2 MAIZE HISTONE GENE PROMOTERS

Protein-DNA interactions in the promoter regions of two maize histone genes have been analyzed by DNase I and DMS in vivo footprinting combi ned with LMPCR amplification. Both promoters present a bimodular struc ture characterized by a proximal cell division-specific set of interac tions and a distal region which displays constitutive footprints but e nhancement of these footprints upon cell proliferation. The inducible region contains two cis-elements common to all replication-dependent p lant histone genes, one of them having previously been shown to be a t arget for the wheat nuclear protein HBP-2. In the constitutive region, the first demonstration for the existence of a transcription factor b inding to the highly conserved plant histone-specific octamer CGCGGATC is provided. Exchange of cell-type-specific factors is postulated to occur at that site. Additional immediate upstream constitutive element s binding regulatory proteins include a degenerate octameric sequence, a CCAAT-box, a CACCC sequence and composite ACGTCA/ACGTGG hexameric s equences binding HBP-1-related trans-acting factors. The close proximi ty of these, elements within the constitutive region and the redundanc y of some of them suggest complex cooperation and competition mechanis ms contributing to achieve the final expression level and likely also to mediate the interplay between constitutive and inducible factors.