TELOMERES - BEGINNING TO UNDERSTAND THE END

Telomeres are the protein-DNA structures at the ends of eukaryotic chr omosomes. In yeast, and probably most other eukaryotes, telomeres are essential. They allow the cell to distinguish intact from broken chrom osomes, protect chromosomes from degradation, and are substrates for n ovel replication mechanisms. Telomeres are usually replicated by telom erase, a telomere-specific reverse transcriptase, although telomerase- independent mechanisms of telomere maintenance exist. Telomere replica tion is both cell cycle- and developmentally regulated, and its contro l is likely to be complex. Because telomere loss causes the kinds of c hromosomal changes associated with cancer and aging, an understanding of telomere biology has medical relevance.