Telomeric repeat from T. thermophila cross hybridizes with human telomeres

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Abstract
The ends (telomeres) of eukaryotic chromosomes must have special features to ensure their stability and complete replication. Studies in yeast1–3, protozoa4–6, slime moulds7,8 and flagellates8,10 show that telomeres are tandem repeats of simple sequences that have a G-rich and a C-rich strand. Mammalian telomeres have yet to be isolated and characterized, although a DNA fragment within 20 kilobases of the telomeres of the short arms of the human sex chromosomes has been isolated11. Recently we showed that a chromosome from the fission yeast Schizosaccharomyces pombe could, in some cases, replicate as an autonomous mini-chromosome in mouse cells12. By extrapolation from other systems1,3,13,14, we reasoned that mouse telomeres could be added to the S. pombe chromosome ends in the mouse cells. On setting out to test this hypothesis we found to our surprise that the telomeric probe used (containing both the S. pombe and Tetrahymena thermophila repeats) hybridized to a series of discrete fragments in normal mouse DNA and DNA from a wide range of eukaryotes. We show here that the sequences hybridizing to this probe are located at the telomeres of most, if not all, human chromosomes and are similar to the Tetrahymena telomeric-repeat component of the probe.