Multiple interactions of the transcription factor YY1 with human histone H4 gene regulatory elements.

Multiple regulatory elements and intricate protein-DNA interactions mediate the transcription of the human histone H4 genes in a cell growth-dependent manner. Upon analysis of the regulatory elements of the FO108 histone H4 gene, we identified several potential YY1 binding sites. In this study, we have analyzed the ability of the transcription factor YY1 to interact at these sites in vitro by using electrophoretic mobility shift assays in combination with oligonucleotide competition and antibody immunoreactivity. We show that YY1 specifically binds transcriptional regulatory elements at -340 nt (site III), -100 nt (site I) and at least two domains within the coding region of the histone H4 gene. To test if these elements were functionally responsive to YY1, we performed transient expression experiments in Drosophila S-2 cells transfected with heterologous reporter gene constructs driven by histone H4 gene segments fused to the thymidine kinase promoter. Co-expression of YY1 stimulated promoter activity of these constructs relative to the reporter construct lacking histone H4 gene fragments. Our results suggest that YY1 contributes to transcriptional regulation of the histone H4 gene through interactions at multiple regulatory elements.