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Telomerase is a ribonucleoprotein (RNP) that is responsible for maintaining the terminal repeats of telomeres in most organisms (15). It acts as an unusual reverse transcriptase (RT), using a small segment of an integral RNA component as template for the synthesis of the dGT-rich strand of telomeres (16).. Telomerase activity has been characterized from a wide range of organisms and genes encoding both the RNA and protein components of the enzyme complex identified (for reviews, see references2 and 41). Telomerase RNAs found in ciliated protozoa, in addition to having a short templating region, share a common secondary structure. Telomerase RNAs from yeasts and mammals are considerably larger and exhibit no evident structural conservation. The catalytic RT protein subunit (TERT), initially purified from Euplotes aediculatus as p123, was subsequently found to be homologous to Est2p, a yeast protein required for telomere maintenance (25, 26, 28). Both proteins possess RT-like motifs, alterations ...

Ciliated protozoan (Tetrahymena vorax), coloured scanning electron micrograph (SEM). Tetrahymena vorax is a fresh water, holotrichous, oligohymenophoran, ciliate. Shown here are 3 cells with nice ciliated pellicle surfaces. Tetrahymena are free-living ciliated protozoa that can switch from commensalistic to pathogenic modes of survival. They are common in freshwater ponds. Tetrahymena species are used as model organisms. Magnification: x260 when shortest axis printed at 25 millimetres. - Stock Image C032/0976

o Dendropsophini Fitzinger, 1843 ,--+--o Sphaenorhynchus Tschudi, 1838 [Dryomelictes Fitzinger, 1843; Dryomelictes Cope, 1865; Hylopsis Werner, 1894; Sphoenohyla Lutz & Lutz, 1938] , , ,-- S. bromelicola (Bokermann, 1966) , , ,-- S. carneus (Cope, 1868) , , ,-- S. dorisae (Goin, 1967) , , ,-- S. lacteus (Daudin, 1801) [Hyla lactea Daudin, 1801; Dryomelictes lactea] , , ,-- S. orophilus (A. Lutz & B. Lutz, 1938) , , ,-- S. palustris Bokermann, 1966 , , ,-- S. pauloalvini Bokermann, 1973 , , ,-- S. planicola (A. Lutz & B. Lutz, 1938) , , ,-- S. platycephalus (Werner, 1894) [Hylopsis platycephalus Werner, 1894] , , ,-- S. prasinus Bokermann, 1973 , , `-- S. surdus (Cochran, 1953) , `--+-- Dendropsophus Fitzinger, 1843 [Lophopus Tschudi, 1838; Hylella Reinhardt & Lütken, 1862 1861; Güntheria Miranda-Ribeiro, 1926] , `--o Xenohyla Izecksohn, 1996 , ,-- X. eugenioi Caramaschi, 2001 , `-- X. truncata Izecksohn, 1996 `--+-- Scinax Wagler, 1830 `--+-- Scarthyla goinorum Duellman & de Sá, 1988 [Hyla ...