Single-molecule biophysics research group

University of California, Berkeley


Protection of Telomeres


Telomeres are long repetitive DNA sequences (in humans 5'-TTAGGG-3') located at the ends of eukaryotic chromosomes (labeled in light blue in the image below).


The gradual shortening of telomeres upon each cell division ultimately triggers cell cycle arrest and apoptosis. Hence telomeres serve as an internal clock in the aging process of an organism. Understanding the details of how this clock works and how it can be reset has broad implications for developmental biology, aging, cancer, and stem cell biology. Telomeric tracts can be replenished by a special reverse transcriptase, telomerase which uses the G-overhang as its substrate. Telomerase is shut-off in early stages of embryogenesis and remains active only in germ-line and stem cells. The upregulation of telomerase in somatic cells is the hallmark of the cancer cell evolution and 80-90% of all human cancers have detectable telomerase activity. Telomeres are protected by a large nucleoprotein complex, shelterin which consists of six core proteins (TRF1, TRF2, TIN2, TPP1, POT1 and RAP1). Shelterin has critical role on protection of telomeres against degradation, DNA damage response pathways and regulation of telomerase activity. We do not have an integrated mechanistic understanding of telomere assembly, how shelterin remodels telomeric DNA and protects against DNA damage response pathways. The major challenges have been the development of a robust in vitro/in vivo experimental geometry and direct imaging tools for the entire process. Recent breakthroughs in the biochemical characterization of purified shelterin components and optical imaging now allow both these bottlenecks to be addressed. Currently we are investigating the effect of morphological changes brought about by the shelterin proteins on telomeres and their influence on protection against DNA damage response pathways by using super resolution microscopy. We are also developing assays to assemble the shelterin complex to gain a better understanding on the interplay between the six core components and their in role in restructuring and maintenance of telomeres. We are also doing single-molecule in-vitro studies on telomerase in order to gain a detailed understanding of the structure and function of the active enzyme.

  Relevant papers
  • Sujay Ray, Jigar N. Bandaria, Mohammad H. Qureshi, Ahmet Yildiz, and Hamza Balci. G-quadruplex formation in telomeres enhances POT1/TPP1 protection against RPA binding. 2014. PNAS 111(8). doi:10.1073 pdf