Human telomerase maintains genome stability by adding telomeric repeats to the ends of linear chromosomes. Although previous studies have revealed profound insights into telomerase functions, the low cellular abundance of functional telomerase and the difficulties in quantifying its activity leave its thermodynamic and kinetic properties only partially characterized. Employing a stable cell line overexpressing both the human telomerase RNA component and the N-terminally biotinylated human telomerase reverse transcriptase and using a newly developed method to count individual extension products, we demonstrate here that human telomerase holoenzymes contain fast- and slow-acting catalytic sites. Surprisingly, both active sites became inactive after two consecutive rounds of catalysis, named single-run catalysis. The fast active sites turned off 40-fold quicker than the slow ones and exhibited higher affinities to DNA substrates. In a dimeric enzyme, the two active sites work in tandem, with the faster site functioning before the slower one, and in the monomeric enzyme, the active sites also perform single-run catalysis. Interestingly, inactive enzymes could be reactivated by intracellular telomerase-activating factors (iTAFs) from multiple cell types. We conclude that the single-run catalysis and the iTAF-triggered reactivation serve as an unprecedented control circuit for dynamic regulation of telomerase. They endow native telomerase holoenzymes with the ability to match their total number of active sites to the number of telomeres they extend. We propose that the exquisite kinetic control of telomerase activity may play important roles in both cell division and cell aging.
Bibliographical noteFunding Information:
This work was supported by Cancer Prevention and Research Institute of Texas Grant RP120474 (to Q.-X. J.) and in part by National Institutes of Health Grants R01GM111367 and R01GM093271 (to Q.-X. J.), Cystic Fibrosis Foundation Grant JIANG15G0 (to Q.-X. J.), Welch Foundation Grant I-1684 (to Q.-X. J.), and startup funds from the University of Florida (to Q.-X. J.). The authors declare that they have no conflicts of interest with the contents of this article. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
3 Supported by K99/R00 Pathway to Independence award from National Insti-tutes of Health NCI Grant KCA197672A.
Acknowledgments—We are indebted to members of the Jiang laboratory and those of the Shay/Wright laboratory. Three members of the Ph.D. thesis committee for M. E. S., Drs. Hamid Mirazei, Robert Eber-hart, and Michael Cho, provided insightful advice and comments. Drs Sixue Chen and Jin Koh in the Proteomics Core at the Interdisciplinary Center of Biotechnology Research (ICBR) of University of Florida offered technical support. Some experiments reported here were performed in a laboratory constructed with support from National Institutes of Health Grant C06RR30414.
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, Non-U.S. Gov't