In the terminal 6–10 kb of a chromosome,
telomeric sequences and telomere-associated
sequences can be differentiated (1). The telomere-
associated sequences contain autonomously
replicating sequences (ARS). The telomere
sequences consist of about 250 to 1500 Grich
repeats (!9 kb). They are highly conserved
among different species (2). Telomerase activity
is essential for survival in protozoans and yeast.
In vertebrates it occurs mainly in germ cells,
and no telomerase activity is found in somatic
tissues. The cell division-dependent decrease of
telomere length is viewed as being related to
aging and death of cells because, ultimately,
functional DNAwill be lost. Unlike normal cells,
many tumors have telomerase activity.
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