Cell
Volume 88, Issue 5, 7 March 1997, Pages 657-666
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Article
Long G Tails at Both Ends of Human Chromosomes Suggest a C Strand Degradation Mechanism for Telomere Shortening

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Abstract

The chromosomes of lower eukaryotes have short telomeric 3′ extensions. Using a primer-extension/nick-translation technique and nondenaturing hybridization, we find long 3′ G-rich tails at human chromosome ends in mortal primary fibroblasts, umbilical vein endothelial cells, and leukocytes, as well as in immortalized fibroblasts. For all cells tested, >80% of the telomeres have long G-rich overhangs, averaging 130–210 bases in length, in disagreement with the conventional model for incomplete lagging-strand replication, which predicts overhangs on 50% of the chromosome ends. The observed G tails must exist during most of the cell cycle and probably result from degradation of both chromosome ends. The average lengths of the G tails are quantitatively consistent with the observed rates of human chromosome shortening.

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