Rescue of an hTERT mutant defective in telomere elongation by fusion with hPot1.

The protein hPot1 shares homology with telomere-binding proteins in lower eukaryotes and associates with single-stranded telomeric DNA in vitro as well as colocalizing with telomere-binding proteins in vivo. We now show that hPot1 is coimmunoprecipitated with telomeric DNA and that stable expression of this protein in telomerase-positive cells results in telomere elongation, supporting the idea that hPot1 is a bona fide mammalian telomere-binding protein. We previously found that mutations in the N-terminal DAT domain of the hTERT catalytic subunit of telomerase rendered the enzyme catalytically active but unable to elongate telomeres in vivo.