Normal human telomeres are not late replicating

Woodring E. Wright, Valerie M. Tesmer, Martha L. Liao, Jerry W. Shay

Research output: Contribution to journalArticlepeer-review

98 Scopus citations


Telomeres in yeast are late replicating. Genes placed next to telomeres in yeast can be repressed (telomere positional effects), leading to the hypothesis that telomeres may be heterochromatic and may control the expression of subtelomeric genes. In addition, yeast telomeres are processed to have a transient long overhang at the end of S phase. The applicability of the yeast data to human biology was examined by determining the timing of telomere replication and processing in normal human diploid fibroblasts. Telomeres were purified from synchronized cells that had been labeled with 5- bromodeoxyuridine (BrdU) at hourly intervals, and the fraction of labeled telomeres was analyzed by retrieval with anti-BrdU antibodies. We determined that normal human telomeres replicate throughout S phase rather than being very late replicating. Furthermore, the overall timing of replication was unaffected by telomere length in young versus old cells or cells whose telomeres had been elongated following transfection with the catalytic subunit of telomerase. Finally, the asymmetry in the length of the G-rich overhang in daughter telomeres produced by leading versus lagging strand synthesis was shown to be established within 1 h of telomere replication, indicating there is no significant delay between synthesis and the processing events that contribute to the establishment of asymmetric overhangs. Therefore, the timings of replication and processing of human telomeres are very different from those of yeast.

Original languageEnglish (US)
Pages (from-to)492-499
Number of pages8
JournalExperimental Cell Research
Issue number2
StatePublished - Sep 15 1999


  • Cellular aging
  • DNA replication
  • Heterochromatin
  • Telomeres

ASJC Scopus subject areas

  • Cell Biology


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