FIG. 4.

POT1^ΔOB, but not POT1^ΔTRF2, acts in a dominant-negative fashion to elongate telomeres. (A) Detection of the indicated FLAG-tagged POT1 (F-POT1) proteins stably expressed in HA1 cells by immunoprecipitation (IP) and immunoblotting (IB) with an anti-FLAG antibody. (B) Telomere length, as assessed by Southern hybridization with a ³²P-labeled telomeric probe, of HA1 cells stably expressing the indicated proteins at PDs 0, 20, and 40. Boxes indicate mean telomere length ± standard deviation calculated from three independently derived sets of cell lines.