Human Telomerase Caught in the Act

Based on prior work, it was expected that telomerase would preferentially elongate the shortest telomeres in a cell, extending the telomeric G-rich strand through a process that is coupled to the synthesis of the complementary strand. Contrary to this view, now show that telomerase in human cancer cells extends most telomeres during every S phase and that complementary strand synthesis does not immediately follow telomerase action.