The objective of this program is to understand the regulation of the cell cycle dependent human histone genes. The coupling of histone gene expression with DNA replication and the stringent requirement of histone proteins to package newly replicated DNA into nucleosomes account for the involvement of histone gene expression in the control of cell growth and cell division. Studies carried out during the current funding period have identified the cell cycle promoter regulatory element of an H4 histone gene and three sites that contribute to level of transcription in vivo and in vitro. We have initiated characterization of two transcription factor complexes that exhibit sequence-specific and phosphorylation-dependent binding to the histone gene cell cycle regulatory element designated Site II. The first is HiNF-D, which includes an RB-related protein, cyclin A and cdc2. The second is a 48 kD protein designated HiNF-M which we have recently purified and shown to be IRF-2, a member of the IRF family that exhibits oncogenic activity. These findings support the concept that the Site II cell cycle regulatory element is multipartite and has structural and functional redundancy that may provide competency for growth control in response to specific physiological signalling pathways operative under diverse biological conditions. Our results also support a mechanism for coordinate transcriptional control of cell cycle regulated H4, H3 and H1 histone genes. A contribution of nuclear architecture to control of H4 histone genes is suggested by association of transcription factors with the nuclear matrix. Based on these results the Specific Aims of our current studies are: 1) to further define and characterize sequences in four regulatory sites of the H4 histone gene promoter that modulate transcription during the cell cycle and during differentiation; 2) to continue the identification, isolation, and characterization of protein factors that interact with histone gene regulatory elements and to define their roles in H4 histone promoter activity; 3) to assess the contributions of factor regulation to the control of histone gene transcription by a) determining the role of phosphorylation and b) cloning cDNAs for studying factor expression; and 4) to examine the involvement of nuclear structure and the nuclear matrix with regulation of histone gene expression. Our working hypothesis is that the integration of activities at multiple histone promoter elements mediates expression in response to a broad spectrum of signalling pathways related to cell cycle and growth control.
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