Interaction of the CCAAT Displacement Protein with Shared Regulatory Elements Required for Transcription of Paired Histone Genes

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Abstract
The H2A and H2B genes of the Xenopus xlh3 histone gene cluster are transcribed in opposite directions from initiation points located approximately 235 bp apart. The close proximity of these genes to one another suggests that their expression may be controlled by either a single bidirectional promoter or by separate promoters. Our analysis of the transcription of histone gene pairs containing deletions and site-specific mutations of intergenic DNA revealed that both promoters are distinct but that they overlap physically and share multiple regulatory elements, providing a possible basis for the coordinate regulation of their in vivo activities. Using the intergenic DNA fragment as a probe and extracts from mammalian and amphibian cells, we observed the formation of a specific complex containing the CCAAT displacement protein (CDP). The formation of the CDP-containing complex was not strictly dependent on any single element in the intergenic region but instead required the presence of at least two of the three CCAAT motifs. Interestingly, similar CDP-containing complexes were formed on the promoters from the three other histone genes. The binding of CDP to histone gene promoters may contribute to the coordination of their activities during the cell cycle and early development.