Switching human telomerase on and off with hPOT1 protein in vitro.
POT1 (protection of telomeres 1) protein binds the G-rich single-stranded telomeric DNA at the ends of chromosomes. In human cells hPOT1 is involved in telomere length regulation, but the mechanism of this regulation remains unknown. Examination of the high-resolution crystal structure of the hPOT1-TTAGGGTTAG complex suggested that it would not be extended by telomerase, a hypothesis that we confirm by in vitro assays with recombinant telomerase. On the other hand, when hPOT1 is bound at a position one telomeric repeat before the 3'-end, leaving an 8-nucleotide 3'-tail, the complex is extended with improved activity and processivity. Thus, depending on its location relative to the DNA 3'-end, hPOT1 can either inhibit telomerase action or form a preferred substrate for telomerase. We propose that another factor catalyzes the interconversion of these states in vivo.[1]References
- Switching human telomerase on and off with hPOT1 protein in vitro. Lei, M., Zaug, A.J., Podell, E.R., Cech, T.R. J. Biol. Chem. (2005) [Pubmed]
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