A second HP1

The packaging of DNA into condensed heterochromatin structures results in gene silencing. Heterochromatin protein 1 (HP1) is located in pericentric heterochromatin and maintains the heterochromatic state by interacting with modified histones and the modifying enzymes. In the early Edition of the Proceedings of the National Academy of Sciences, Christopher Shaffer and colleagues report the discovery of a second heterochromatin protein in Drosophilamelanogaster (PNAS, DOI/10.1073/pnas.212458899, October 7, 2002).

Shaffer et al. used the yeast two-hybrid assay to search for HP1-interacting proteins and identified HP2. The C-terminal region of HP1 is required for the interaction with HP2. The HP2 protein is a large chromosomal protein with two AT-hook regions and it is co-distributed with HP1 in pericentric heterochromatin. They cloned the Drosophila HP2 gene and demonstrated that mutation of the gene encoding HP-2 results in suppression of position effect variegation (PEV).