Telomerase RNA is an integral part of telomerase, the ribonucleoprotein enzyme that catalyzes the synthesis of telomeric DNA. The RNA moiety contains a templating domain that directs the synthesis of a species-specific telomeric repeat and may also be important for enzyme structure and/or catalysis. Phylogenetic comparisons of telomerase RNA sequences from various Tetrahymena spp. and hypotrich ciliates have revealed two conserved secondary structure modelsthat share many features. We have cloned and sequenced the telomerase RNA genes from an additional six Tetrahymena spp. (T.vorax, T.borealis T.australis, T silvana T capricornis and T.paravorax). inclusion of these sequences, most notably that from T paravorax, in a phylogenetic comparative analysis allowed us to more narrowly define structural elements that may be necessary for a minimal telomerase RNA. A primary sequence element, positioned 5' of the template and conserved between all previously known ciliate telomerase RNAs, has been reduced from 5'-(C)UGUCA-3'to the 4 nt sequence 5'-GUCA-3'. Conserved secondary structural features and the impact they have on the general organization of ciliate telomerase RNAs is discussed.
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We gratefully acknowledge the assistance given by Drs Ellen Simon (University of Illinois) and Howard Buhse (University of Illinois, Chicago) in providing various Tetrahymena spp. We thank Drs Colin Campbell, Paul Siliciano and Karin Musier-Forsyth for critical reading of and helpful comments on the manuscript. This research was supported in part by the Minnesota Medical Foundation, an American Cancer Society Institutional Research Grant and United States Public Health Services grant GM 50861 to DPR.