EGD2 is a conserved telomere binding protein

Author

Amrita Biswas, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2012

Degree Name

Master of Science

Department

Molecular Biology Microbiology and Biochemistry

First Advisor

Weilbaecher, Rodney

Abstract

Telomeres are essential for the stability of the eukaryotic genome. Disruption of telomere function leads to chromosomal abnormalities and is implicated in human cancer and aging. The simple guanine-rich repeats of telomeres are maintained by telomerase, and several telomere binding proteins are known to regulate telomerase activity. The extreme terminus of the guanine-rich strand, the substrate to which telomerase must gain access and extend, exists as a single-strand overhang that varies in length in step with the cell cycle. In vitro these telomeric single strand sequences readily adopt guanine-quadruplex structures which purified telomerase has reduced ability to bind for extension. S. cerevisiae Cdc13 is one of several telomeric proteins known to melt telomeric guanine-quadruplexes and thereby promote telomerase activity in vitro. Our lab identified a human nuclear protein with DNA binding properties similar to S. cerevisiae Cdc13; namely, the ability to bind and melt telomeric G-quadruplexes and purine motif triplexes in vitro. The activity was purified and identified as the nascent polypeptide associated complex (NAC), a heterodimer comprised of NACa; and BTF3 subunits. The goal of the present study was to determine whether or not the S. cerevisiae homologues of NAC (Egd2) and BTF3 (Egd1) are enriched at telomeres in vivo, and if so, to characterize NAC's function at the telomere. Our study demonstrates that S. cerevisiae Egd2 is preferentially enriched at telomeres, although evidence for Egd1 enrichment at telomeres was not observed. This may indicate that an Egd2 homodimer, rather than an Egd2-Egd1 heterodimer, localizes to telomeres. Preliminary data demonstrates that EGD2 dosage affects telomere length homeostasis, albeit modestly. Overexpression of EGD2 slightly lengthens telomeres, while egd2- strains have slightly shortened telomeres. Whether the alteration in telomere length is a direct effect of Egd2 function at the telomere is an important, but unresolved question.