The Day Lab investigates the molecular role of G quadruplex DNA in genome stability and human disease. G quadruplexes are non-canonical DNA structures that form readily in repetitive, guanine-rich sequences. While they play an important role in normal cellular physiology, G quadruplexes also trigger genome instability and are associated with cancer. Our lab studies the genetic mechanisms that control G quadruplex formation in vivo with a focus on mammalian telomeres, repetitive sequences that contain abundant quadruplexes. We have a particular focus on alternative mechanisms of telomere maintenance that are activated in ~10% of all tumors and confer poor prognosis. We use a variety of experimental approaches including biochemistry, molecular and cell biology, genetics, and computational biology. The broad, long-term goals of our research are to leverage a fundamental understanding of G quadruplex biology to design therapeutic strategies for malignant disease.