Purification of the human histone H4 gene-specific transcription factors H4TF-1 and H4TF-2.

Transcription of the cell-cycle-regulated human histone genes increases approximately fivefold during S phase. One step toward the elucidation of the biochemical mechanisms that govern cell-cycle-regulated expression of these genes is to purify and characterize the transcription factors that regulate these promoters. Here, we describe the purification of two previously identified factors, H4TF-1 and H4TF-2, which bind the human histone H4 promoter. Purification was achieved through a combination of ion-exchange and oligonucleotide affinity chromatography. On the basis of analysis of purified fractions by SDS-polyacrylamide gels and UV cross-linking, we believe that H4TF-1 is two polypeptides of 105 and 110 kD. This factor binds to a GC-rich DNA sequence required for maximal expression of the H4 gene but does not bind to any Sp1 consensus elements tested. H4TF-2 is a 65-kD protein that binds specifically to sequences within that highly conserved H4 subtype-specific consensus promoter element. Both highly purified factors activated transcription in vitro only from H4 promoters that contained their binding sequences, demonstrating that H4TF-1 and H4TF-2 are H4-specific transcription factors that potentiate expression of this gene.