Telomere end-binding proteins control the formation of G-quadruplex DNA structures in vivo

Katrin Paeschke^1, 3, Tomas Simonsson^2, 3, Jan Postberg¹, Daniela Rhodes² & Hans Joachim Lipps¹

¹  Institute of Cell Biology, University Witten/Herdecke, Stockumer Strasse 10, 58453 Witten, Germany.

²  Medical Research Council, Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.

³  These authors contributed equally to this work.

Telomere end-binding proteins (TEBPs) bind to the guanine-rich overhang (G-overhang) of telomeres. Although the DNA binding properties of TEBPs have been investigated in vitro, little is known about their functions in vivo. Here we use RNA interference to explore in vivo functions of two ciliate TEBPs, TEBP and TEBP. Silencing the expression of genes encoding both TEBPs shows that they cooperate to control the formation of an antiparallel guanine quadruplex (G-quadruplex) DNA structure at telomeres in vivo. This function seems to depend on the role of TEBP in attaching telomeres in the nucleus and in recruiting TEBP to these sites. In vitro DNA binding and footprinting studies confirm the in vivo observations and highlight the role of the C terminus of TEBP in G-quadruplex formation. We have also found that G-quadruplex formation in vivo is regulated by the cell cycle−dependent phosphorylation of TEBP.

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