Human Homolog of Drosophila Heterochromatin-Associated Protein 1 (HP1) Is a DNA-Binding Protein Which Possesses a DNA-Binding Motif with Weak Similarity to That of Human Centromere Protein C (CENP-C)

Heterochromatin-associated protein 1 (HP1) is a nonhistone chromosomal component tightly associated with the pericentromeric heterochromatic region of fruit fly, mouse, and human throughout the cell cycle. Drosophila HP1 has been shown to be involved in position effect variegation and to be required for the correct chromosome segregation in vivo, while the biological activity of human homolog (HP1hsa) has not yet been characterized. We previously reported that human CENP-B and CENP-C, two major centromere heterochromatin autoantigens often recognized by autosera in scleroderma patients, possess DNA-binding activity in vitro. Here, we show that human HP1 which is also an autoantigen targeted by some types of anticentromere autosera, is a DNA-binding protein. Human HP1 was expressed as a GST-fusion in Escherichia coli and purified with glutathione-Se pharose. The DNA-binding activity of the recombinant HP1 was demonstrated by gel mobility shift assay and South-Western-type blotting. The minimum DNA-binding region was further limited to the internal 64-amino acid stretch that is less-conserved between human and fruit fly but retains a helix-enriched motif with weak similarity to CENP-C. This suggests that HP1 is involved in the pericentromeric heterochromatin formation by directly associating with genomic DNA.