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Nature Structural & Molecular Biology 15, 598–604 (1 June 2008) | doi:10.1038/nsmb.1422

Telomerase recruitment by the telomere end binding protein-|[beta]| facilitates G-quadruplex DNA unfolding in ciliates

Katrin Paeschke , Stefan Juranek , Tomas Simonsson , Anne Hempel , Daniela Rhodes & Hans Joachim Lipps

The telomeric G-overhangs of the ciliate Stylonychia lemnae fold into a G-quadruplex DNA structure in vivo. Telomeric G-quadruplex formation requires the presence of two telomere end binding proteins, TEBPα and TEBPβ, and is regulated in a cell-cycle dependent manner. Unfolding of this structure in S phase is dependent on the phosphorylation of TEBPβ. Here we show that TEBPβ phosphorylation is necessary but not sufficient for a G-quadruplex unfolding rate compatible with telomere synthesis. The telomerase seems to be actively involved in telomeric G-quadruplex DNA structure unfolding in vivo. Significantly, the telomerase is recruited to telomeres by phosphorylated TEBPβ, and hence telomerase recruitment is cell-cycle regulated through phosphorylation. These observations allow us to propose a model for the regulation of G-quadruplex unfolding and telomere synthesis during the cell cycle.