Figure 1.

Model for evolution of telomerase and telomere-associated components from group II retrotransposons and DNA repair proteins. After chromosome linearization by the insertion of group II retrotransposons, telomerase and DNA repair proteins evolved roles in telomere maintenance and end protection. Telomere-associated factors also participate genome-wide in transcription, replication, and repair. Other factors function in mitochondria to modulate the response to oxidative stress. Whether the mitochondrial functions of telomere proteins reflect an ancient or newly evolved function is unknown (see text for details).