Abstract
A report in this week's issue by [ Nakamura et al .][1] reports the sequence of telomerase, the enzyme that synthesizes the specialized structures on the ends of chromosomes, from fission yeast and humans, complementing an earlier [report][2] from the same group reporting this sequence from Euplotes and baker's yeast. All four sequences show that these enzymes closely resemble the reverse transcriptases, which synthesize DNA from RNA. In his Perspective, Eickbush argues that telomerases may have evolved from early retrotransposons, DNA elements that can autonomously move around the genome. [1]: http://www.sciencemag.org/cgi/content/short/277/5328/955 [2]: http://www.sciencemag.org/cgi/content/short/276/5312/561