Originally published as Genetics Published Articles Ahead of Print on October 9, 2008.

Genetics, Vol. 180, 1869-1875, December 2008, Copyright © 2008
doi:10.1534/genetics.108.095547

Loss of the Histone Variant H2A.Z Restores Capping to Checkpoint-Defective Telomeres in Drosophila

Yikang S. Rong1

Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892

1 Address for correspondence: National Institutes of Health, Bldg. 37, Room 6056, 37 Convent Dr., Bethesda, MD 20892.
E-mail: rongy{at}mail.nih.gov

The conserved histone variant H2A.Z fulfills many functions by being an integral part of the nucleosomes placed at specific regions of the genome. Telomeres cap natural ends of chromosomes to prevent their recognition as double-strand breaks. At yeast telomeres, H2A.Z prevents the spreading of silent chromatin into proximal euchromatin. A role for H2A.Z in capping, however, has not been reported in any organism. Here, I uncover such a role for Drosophila H2A.Z. Loss of H2A.Z, through mutations in either its gene or the domino gene for the Swr1 chromatin-remodeling protein, suppressed the fusion of telomeres that lacked the protection of checkpoint proteins: ATM, ATR, and the Mre11–Rad50–NBS complex. Loss of H2A.Z partially restores the loading of the HOAP capping protein, possibly accounting for the partial restoration in capping. I propose that, in the absence of H2A.Z, checkpoint-defective telomeres adopt alternative structures, which are permissive for the loading of the capping machinery at Drosophila telomeres.