Interaction of Heterochromatin Protein 2 with HP1 defines a novel HP1 binding domain

摘要

Heterochromatin Protein 2 (HP2) is a nonhistone chromosomal protein from Drosophila melanogaster localized principally in the pericentric heterochromatin, telomeres, and fourth chromosome, all regions associated with HP1. Mutations in HP2 can suppress position effect variegation, indicating a role in gene silencing and heterochromatin formation [Shaffer, C.D. et al. (2002) Proc. Natl. Acad. Sci. 99, 14332-14337]. In vitro coimmunoprecipitation experiments with various peptides from HP2 have identified a single HP1 binding domain. Conserved domains in HP2, including those within the HP1 binding region, have been identified by recovering and sequencing Su(var)2-HP2 from D. willistoni and D. virilis, as well as examining available sequence data from D. pseudoobscura. A PxVxL motif, shown to be an HP1 binding domain in many HP1-interacting proteins, is observed but is not well conserved in location and sequence, and does not mediate HP2 binding to HP1. The sole HP1 binding domain is composed of two conserved regions of 12 and 16 amino acids separated by 19 amino acids. Site-directed mutagenesis within the two conserved regions has shown that the 16 amino acid domain is critical for HP1 binding. This constitutes a novel domain for HP1 interaction, providing a critical link for heterochromatin formation in Drosophila.