The Drosophila HOAP protein is required for telomere capping.

HOAP (HP1/ORC-associated protein) has recently been isolated from Drosophila melanogaster embryos as part of a cytoplasmic complex that contains heterochromatin protein 1 (HP1) and the origin recognition complex subunit 2 (ORC2). Here, we show that caravaggio, a mutation in the HOAP-encoding gene, causes extensive telomere-telomere fusions in larval brain cells, indicating that HOAP is required for telomere capping. Our analyses indicate that HOAP is specifically enriched at mitotic chromosome telomeres, and strongly suggest that HP1 and HOAP form a telomere-capping complex that does not contain ORC2.