PROJECT SUMMARY/ABSTRACT
All genetic information is stored in DNA that is intricately wrapped by proteins to form chromosomes.
Telomeres are the nucleoprotein complexes that cap and protect the ends of chromosomes to prevent them from
fraying, fusing together, and degrading. In addition to capping and protecting the ends of chromosomes,
telomeres regulate the recruitment of telomerase, a specialized enzyme that synthesizes telomere DNA to
collaborate with replicative polymerases and ensure complete chromosome replication. Over the past several
years, multiple single nucleotide polymorphisms have been identified in the genes of telomere end-binding
proteins in patients diagnosed with a range of disorders, including many different types of cancer. These
observations indicate that subtle changes in the structure and/or function of telomere proteins contributes to
genome instability. POT1 (Protection of Telomeres 1) is the most mutated telomere protein associated with
human disorders. POT1 forms a heterodimeric complex with another telomere end-binding protein, TPP1, to
perform diverse but equally critical functions. Specifically, POT1-TPP1 binds to the extreme 3’ end of telomeres
and helps to resolve DNA secondary structure, to recruit telomerase to the telomere, and regulate telomerase-
mediated telomere synthesis. In addition, the POT1-TPP1 proteins shield telomere DNA from being recognized
and repaired by DNA damage machinery. Finally, the POT1-TPP1 heterodimer exhibits extraordinary sequence
specificity that provides discrimination against binding to RNA or to DNA with non-telomere sequence. The
objective of the present proposal is to investigate the multiple and diverse roles of POT1-TPP1 in telomere
maintenance. We will further interrogate the intricate details of telomerase-mediated extension of telomere DNA
and identify how changes in nucleotide pools affect telomerase function and fidelity. Additionally, we will examine
the role of FDA-approved and developing nucleotide and nucleoside analogs in telomerase rates and fidelity. To
accomplish these objectives, we combine structure-function studies to determine the molecular interactions that
dictate POT1-TPP1 function and we corroborate the mechanistic studies with cellular outcome. The results from
this investigation will reveal both structural and functional alterations introduced by pathogenic mutations and
drug administration and will be used to better understand the diverse functions of specialized telomere proteins
and telomerase in maintaining telomere integrity and genomic stability. The project includes a translational
component as we will define the understudied contributions that chemotherapeutic and antiviral agents have on
telomere integrity. On a fundamental level, the work performed in this study will shed light on the assembly,
organization, and functional motions that regulate chromosome end protection.