CILIATE TELOMERASE RNA STRUCTURAL FEATURES

Telomerase RNA is an integral part of telomerase, the ribonucleoprotei n 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 structu re and/or catalysis. Phylogenetic comparisons of telomerase RNA sequen ces from various Tetrahymena spp, and hypotrich ciliates have revealed two conserved secondary structure models that 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 analysi s allowed us to more narrowly define structural elements that may be n ecessary for a minimal telomerase RNA, A primary sequence element, pos itioned 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 t he impact they have on the general organization of ciliate telomerase RNAs is discussed.