Telomere Length Analysis and In Vitro Telomerase Assay

Barring exceptional instances, the DNA contained in eukaryotic chromosomes is linear. Linearity of the chromosomal DNA and the compartmentalized architecture of the eukaryotic cell are the two principle features that distinguish the prokaryotes from the eukaryotes and that have facilitated the evolution of totally different strategies for interaction with other species and the environment. Major changes in strategy that were made possible by linearity of chromosomes were an enormous increase in the information content of the genome and the development of sexuality as a means for efficient exchange of genetic information (1 ). But linear chromosomes have ends, and the presence of ends produced two major biological problems. One problem was identified early by Muller (2 ,3 ) and by McClintock (4 ), as the requirement to protect natural ends of chromosomes from fusion and recombination with other chromosomes and from exonucleolytic erosion. It was thus recognized that the ends of chromosomes must have specialized structural and functional features required for chromosome stability. We know today that another potential cause of chromosomal instability that must be dealt with is that unless it is protected, a DNA end will be recognized as damaged DNA that the cell will attempt to heal with ensuing loss of chromosome integrity and cell viability.