Conserved sequence elements in human main type-H1 histone gene promoters: their role in H1 gene expression.

In man, the H1 class of histones consists of seven different isoforms, termed H1.1-H1.5, H1t and H1o. Analysis of the promoters of the respective genes reveals that all seven H1 gene promoters share conserved sequence elements: a TATA box at around position -25 (relative to the transcription start site), a CCAAT motif at about position -50 (except in the H1 promoter), an H1-box (AAACACA) around position -110 (except in the H1.1 promoter), and the highly conserved motif TGTGT/CTA (TG-box or CH1UE) at around nucleotide position -450 (except in the H1.1 promoter). Analysis of the H1.3 gene promoter was carried out with reporter gene assays (using the luciferase gene as a reporter gene) including stepwise deletion and site-directed mutagenesis. In addition, electrophoretic mobility-shift assays were carried out for the analysis of protein/DNA interactions at conserved promoter motifs. Mutation analysis indicates that the CH1UE motif is involved in mediating the S-phase-dependent expression of the H1.3 gene. Comparison of H1 promoters shows that the CCAAT-box is extended in each case by CA. Mutational analysis indicates that only the CCAATCA heptanucleotide, but not just the CCAAT sequence mediates the effect of this element in H1 gene promoters.