Isolation and characterization of a human telomere

A method is described that allows cloning of human telomeres in S. cerevisiae by joining human telomeric restriction fragments to yeast artificial chromosome halves. The resulting chimeric yeast-human chromosomes propagate as true linear chromosomes, demonstrating that the human telomere structure is capable of functioning in yeast and suggesting that telomere functions are evolutionarily conserved between yeast and human. One cloned human telomere, yHT1, contains 4 kb of human genomic DNA sequence next to the tandemly repeating TTAGGG hexanucleotide. Genomic hybridizations using both cloned DNA and TTAGGG repeats have revealed a common structural organization of human telomeres. This 4 kb of genomic DNA sequence is present in most, but not all, human telomeres, suggesting that the region is not involved in crucial chromosome-specific functions. However, the extent of common features among the human telomeres and possible similarities in organization with yeast telomeres suggest that this region may play a role in general chromosome behavior such as telomere-telomere interactions. Unlike the simple telomeric TTAGGG repeats, our cloned human genomic DNA sequence does not cross-hybridize with rodent DNA. Thus, this clone allows the identifications of the terminal restriction fragments of specific human chromosomes in human-rodent hybrid cells.