Telomere maintenance mechanisms and cellular immortalization

Immortal cell populations are able to proliferate indefinitely. Immortaliza tion is associated with activation of processes that compensate for the tel omeric shortening that accompanies cell division in normal somatic cells. I n many immortal cell lines, telomere maintenance is provided by the action of the ribonucleoprotein enzyme complex, telomerase. Some immortal cell lin es have undetectable or very low levels of telomerase activity and there is evidence that these cells maintain their telomeres by an alternative mecha nism.