Histone H1 binds to the putative nuclear factor I recognition sequence in the mouse alpha 2(I) collagen promoter.

It has previously been demonstrated that nuclear factor I (NF I) or a related protein binds to a region between -315 and -295 from the start of transcription in the mouse alpha 2(I) collagen gene promoter. In the present work we have purified this factor to homogeneity from rat liver. DNA sequence-specific proteins were isolated from nuclear extracts using heparin-agarose affinity chromatography and two successive chromatographies on a recognition site affinity matrix. Approximately 160 micrograms of the DNA binding proteins was obtained from 100 g of rat liver. More than 1700-fold purification over the nuclear extract and 58% recovery of the DNA binding activity was achieved. The purified preparation contained five to six protein components ranging in molecular weight from 30,000 to 35,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was demonstrated using DNase I footprint analysis that the factor binds to the putative NF I binding site in the mouse alpha 2(I) collagen promoter. It has a dissociation constant of 7 nM for a short DNA fragment containing this binding site, while a constant of 0.45 nM was obtained for a similar-sized fragment containing the nuclear NF I consensus binding sequence. The purified factor is identical to histone H1 in several respects. They share similar amino acid compositions and they give similar V8-protease and N-bromosuccinimide peptides. In addition, antibodies raised to bovine histone H1 recognize the purified factor and interfere with its binding to DNA. Methylation interference and preparative gel shift assay show that histone H1 binds to the specific sequence from the preparation of the alpha 2(I) collagen promoter binding factor. It is thus evident from the present results, that histone H1 binds to the NF I recognition sequence in the mouse alpha 2(I) collagen promoter.