The Ku heterodimer is one such protein with dual roles at broken and telomeric ends. Ku is a high affinity DNA end binding complex critical for DNA DSB repair via nonhomologous end joining (NHEJ) and, surprisingly, multiple aspects of telomere biology. Previous work by us and others has firmly established that Ku performs separable activities at DSBs versus telomeres, however the mechanisms of action at these sites have yet to be fully elucidated. Ku is also a principal mediator of the catastrophic end-to-end fusions that can occur at dysfunctional telomeres. How Ku's NHEJ activity is inhibited at wild type telomeres remains poorly defined. We are pursuing the answers to these questions in Saccharomyces cerevisiae, a genetically tractable model organism, which has contributed greatly to our current understanding of telomere biology and DNA DSB repair. Through comprehensive site-directed mutagenesis of the yeast Ku70 and Ku80 subunit genes, we have proposed a 'two-face' model for Ku's functions at DSBs versus telomeres - whereby there is an outward face that mediates NHEJ and an inward face that mediates Ku's telomeric functions. Our current work seeks to test and expand various aspects of this model and to elucidate the molecular determinants of Ku's ability to protect telomeric ends from repair activities. Most recently, we have translated our work on Ku in yeast to human cells, proposing an additional mechanism by which human telomeres are prevented from being engaged in NHEJ.

In addition, my laboratory studies the mechanisms of telomere dysfunction in the bone marrow failure- and cancer-predisposition syndrome, dyskeratosis congenita (DC). The underlying cellular pathology in DC is a defect in telomere maintenance. In many cases, the defect arises from mutations in genes encoding components of telomerase, the telomere replication enzyme, or proteins that are required for normal telomerase biogenesis or stability. Mutations in these genes results in decreased telomerase activity and resultant telomere shortening over generations. TINF2 is the second most commonly mutated gene identified in the disorder and encodes a protein that binds to telomeres. Mutations in TINF2 most often result in dramatically short telomeres in a single generation by an unknown mechanism. My laboratory is studying how TINF2 mutations impact telomeres and the genetic basis of telomere dysfunction in patients with DC who appear to lack mutations in the known DC-associated genes.