ARCHITECTURE OF TELOMERASE RNA

Telomerase, an essential ribonucleoprotein reverse transcriptase, adds telomeric DNA to the ends of eukaryotic chromosomes, We examined the conformational properties of the naked RNA moiety of telomerase from t wo related ciliates, Tetrahymena thermophila and Glaucoma chattoni. As well as finding evidence for features proposed previously on the basi s of phylogenetic comparisons, novel conserved structural properties w ere revealed. Specifically, although the region around helix III was p reviously proposed to form a pseudoknot, our results indicate that in the naked RNA this region maintains a level of 'plasticity', probably in an equilibrium favoring one of two helices, In addition, these stud ies reveal that the templating domain is not entirely single-stranded as previously proposed, but is ordered due to constraints imposed by o ther parts of the RNA, Finally, our results suggest that the GA bulge in helix IV may introduce a structurally conserved kink, We now propos e a 'two-domain' structure for the telomerase RNA based on function: o ne conformationally flexible domain, which includes the template and t he region around helix III, involved with enzymatic function, and a se cond largely helical domain, including helices I and IV and the propos ed kink, which may serve as a scaffold for protein binding.