Constitutive and cell-division-inducible protein-DNA interactions in two 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 combined with LMPCR amplification. Both promoters present a bimodular structure characterized by a proximal cell division-specific set of interactions and a distal region which displays constitutive footprints but enhancement of these footprints upon cell proliferation. The inducible region contains two cis-elements common to all replication-dependent plant histone genes, one of them having previously been shown to be a target for the wheat nuclear protein HBP-2. In the constitutive region, the first demonstration for the existence of a transcription factor binding 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 elements binding regulatory proteins include a degenerate octameric sequence, a CCAAT-box, a CACCC sequence and composite ACGTCA/ACGTGG hexameric sequences binding HBP-1-related trans-acting factors. The close proximity of these elements within the constitutive region and the redundancy of some of them suggest complex cooperation and competition mechanisms contributing to achieve the final expression level and likely also to mediate the interplay between constitutive and inducible factors.