THE RNA COMPONENTS OF HUMAN AND MOUSE TELOMERASES

Because conventional DNA polymerases synthesize DNA unidirectional wit h a 5' to 3' polarity and require an RNA primer, telomeric DNA at chro mosome ends is not completely replicated, leading to an end-replicatio n problem. Most immortal eukaryotic cells can fully replicate chromoso me ends by expressing the enzyme telomerase, a ribonucleoprotein that uses an RNA template to add new telomeric repeats to the chromosome en ds. Recently, the RNA components of human and mouse telomerases have b een cloned, leading to new insights into the expression and regulation of telomerase in both normal and cancer cells. Experiments with the h uman telomerase RNA indicate the telomerase is essential for the long- term growth of cancer cells. These findings further support our belief that telomerase is an excellent target for a novel class of cancer th erapeutics.