Evolutionary conservation and functional synergism of curved DNA at the mouse epsilon- and other globin-gene promoters.

Human and mouse globin genes were separated approximately 200 million years ago but still share homology and synergism in many aspects including DNA structure. We first mapped DNA bend sites in the mouse epsilon-globin gene and found that these sites were distributed in a regular manner except in the coding region and their overall average distance was 650.7 bp. The first bend site upstream of the cap site (MepsilonB-1, -334 to -147 bp) was found to contain A + T-rich sequences and features contributing to DNA curvature by computer analysis. Transcription assays using deletion constructs indicated strong promoter activity up to bp -215 in erythriod K562 cells. Therefore, the MepsilonB-1 site was located immediately upstream of the promoter region. A reporter gene assay using a series of constructs containing the promoter region revealed that the MepsilonB-1 site showed repressor activity, and on replacement of the DNA curvature with one from another source the activity was retained. A similar feature was found in the other conserved B-1 sites in the human, bovine, and rabbit beta-like globin genes, with the exception of an unconserved B-1 site in the chicken beta-globin gene. A common feature of these conserved B-1 sites was not the nucleotide sequences but the DNA curvature. Furthermore, a unique nucleosome phase at the MepsilonB-1 site was likely to be directed by DNA curvature. Based on these results, DNA curvature is one of the major features of these promoter regions which might influence transcription through nucleosome positioning.