Telomeric overhang length determines structural dynamics and accessibility to telomerase and ALT-associated proteins.
The G-rich single-stranded DNA at the 3' end of human telomeres can self-fold into G-quaduplex (GQ). However, telomere lengthening by telomerase or the recombination-based alternative lengthening of telomere (ALT) mechanism requires protein loading on the overhang. Using single-molecule fluorescence spectroscopy, we discovered that lengthening the telomeric overhang also increased the rate of dynamic exchanges between structural conformations. Overhangs with five to seven TTAGGG repeats, compared with four repeats, showed much greater dynamics and accessibility to telomerase binding and activity and loading of the ALT-associated proteins RAD51, WRN, and BLM. Although the eight repeats are highly dynamic, they can fold into two GQs, which limited protein accessibility. In contrast, the telomere-specific protein POT1 is unique in that it binds independently of repeat number. Our results suggest that the telomeric overhang length and dynamics may contribute to the regulation of telomere extension via telomerase action and the ALT mechanism.
Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA; Medical Scholars Program, University of Illinois, 506 South Matthews Avenue, Urbana, IL 61801, USA.
Helen
H
Hwang
Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA.
Alex
A
Kreig
Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA.
Jacob
J
Calvert
Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Suite 326, BRIDG, Pittsburgh, PA 15219, USA.
Justin
J
Lormand
Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, P.O. Box 208024, New Haven, CT 06520, USA.
Yongho
Y
Kwon
Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, P.O. Box 208024, New Haven, CT 06520, USA.
James M
JM
Daley
Department of Molecular Biophysics and Biochemistry, Yale University, 333 Cedar Street, P.O. Box 208024, New Haven, CT 06520, USA.
Patrick
P
Sung
Department of Environmental and Occupational Health, University of Pittsburgh, 100 Technology Drive, Suite 326, BRIDG, Pittsburgh, PA 15219, USA.
Patricia L
PL
Opresko
Bioengineering Department, University of Illinois, 1304 West Springfield Avenue, Urbana, IL 61801, USA; Institute for Genomic Biology, University of Illinois, 1206 West Gregory Street, Urbana, IL 61801, USA; Physics Frontier Center (Center of Physics for Living Cells), University of Illinois, 1110 West Green Street, Urbana, IL 61801, USA. Electronic address: smyong@illinois.edu.
Sua
S
Myong
D001483:Base Sequence; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D054856:G-Quadruplexes; D006801:Humans; D056004:Molecular Dynamics Simulation; D051135:Rad51 Recombinase / Q000378:metabolism; D053484:RecQ Helicases / Q000378:metabolism; D000089804:Shelterin Complex; D020080:Tandem Repeat Sequences; D019098:Telomerase / Q000378:metabolism*; D016615:Telomere / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D059505:Telomere Homeostasis; D034501:Telomere-Binding Proteins / Q000378:metabolism; D000071657:Werner Syndrome Helicase
D018076:DNA, Complementary; C440849:POT1 protein, human; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D019098:Telomerase; D005090:Exodeoxyribonucleases; C097151:Bloom syndrome protein; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase