A gene-specific promoter element is required for optimal expression of the histone H1 gene in S-phase.

An H1 gene-specific element (H1-box, 5'-AAACACA-3') modulates S-phase expression of the gene in vivo as judged by analysis of transcripts from histone genes transfected into HeLa cells. Deletion or base-substitution of the element causes a 15- to 30-fold decrease in steady-state H1 mRNA levels in randomly growing cells and eliminates cell cycle control of transcription in synchronized cells. Mutations within the H1-specific element which abolish S-phase control of transcription also eliminate binding of a sequence-specific nuclear factor capable of binding specifically to this region in vitro. Transfection of multiple copies of H1-box elements into cells drastically decreases H1 mRNA levels, mimicking the effect observed when the motif is rendered non-functional by deletion or substitution mutagenesis. In contrast, introduction of mutated H1 elements into cells has no detectable effect. Together, these results imply that an interaction between the H1-box and a sequence-specific trans-acting factor modulates transcriptional control of H1 genes in vivo.