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Zaug, AJ, Podell, ER and Cech, TR (2005) Human POT1 disrupts telomeric G-quadruplexes allowing telomerase extension in vitro. Proc. Natl. Acad. Sci. U.S.A. 102:10864-9


The POT1 (protection of telomeres 1) protein binds the ssDNA overhangs at the ends of chromosomes in diverse eukaryotes. POT1 is essential for chromosome end-protection, as best demonstrated in fission yeast. In human cells, hPOT1 is also involved in telomere-length regulation. We now show that telomeric oligonucleotides, such as d[GGG(TTAGGG)(3)], which form intramolecular G-quadruplexes through Hoogsteen base-pairing, serve as only marginal primers for extension by recombinant human telomerase; telomerase stalls after every nucleotide addition. Addition of hPOT1 to the reaction restores the normal processive elongation pattern seen with primers that cannot form G-quadruplexes. hPOT1 does not act catalytically but, instead, forms a stoichiometric complex with the DNA, freeing its 3' tail. An antisense oligonucleotide, which base-pairs near the 5' end of the telomeric sequence, leaving a telomerase-extendable 3' tail, duplicates the effect of hPOT1 on activation of G-quadruplex primers. Thus, hPOT1 may function simply by trapping the unfolded forms of these telomeric primers in an equilibrium population. We propose an additional role for hPOT1 in telomere maintenance: disrupting G-quadruplex structures in telomeric DNA, thereby allowing proper elongation by telomerase.


PubMed PMC1180509 Online version:10.1073/pnas.0504744102


Base Sequence; DNA/chemistry; DNA/genetics; DNA/metabolism; DNA Primers/genetics; DNA-Binding Proteins/genetics; DNA-Binding Proteins/metabolism; Humans; Macromolecular Substances; Models, Biological; Nucleic Acid Conformation; Recombinant Proteins/genetics; Recombinant Proteins/metabolism; Telomerase/genetics; Telomerase/metabolism; Telomere/metabolism; Telomere-Binding Proteins/genetics; Telomere-Binding Proteins/metabolism