Telomeres are the repetitive G rich DNA sequences at the end of chromosomes and shorten at each round of cell division. Besides the incomplete DNA synthesis, single and double DNA strand breaks, if not repaired, also contribute to the telomere shortening. To assess the frequency of strand breaks in proliferating Hela cells, telomere fragments were released by alkaline denaturing and electrophoresis from cells embedded in agarose, blotted onto membrane, and detected by probe specific to telomere sequence. The quantity of telomere fragments released was estimated to be less than 0.4% of the total telomere content, which corresponded to less than one break per cell. Since the mean length of the terminal restriction fragments of the cells was about 7 kbp, the fragments detected would lead to less than 19 bp in mean telomere shortening.
