RESUMO
The phylogenetic relationships between ciliate species in the suborder Tetrahymenina, order Hymenostomata, was investigated by comparing their telomerase RNA (TER) sequences. This relatively small RNA is an integral part of telomerase, the ribonucleoprotein enzyme that catalyses the synthesis of telomeric DNA. Despite a relatively rapid rate of primary sequence divergence, conserved functional and structural elements within TERs facilitate the accurate alignment of truly homologous nucleotides. The tetrahymenine phylogeny derived from distance analysis of TER sequences is largely consistent with those based on rRNA and histone sequences.
Assuntos
RNA de Protozoário/genética , Telomerase/genética , Tetrahymenina/classificação , Tetrahymenina/enzimologia , Animais , Sequência de Bases , DNA de Protozoário/genética , Genes de Protozoários , Dados de Sequência Molecular , Conformação de Ácido Nucleico , Filogenia , RNA de Protozoário/química , Especificidade da Espécie , Tetrahymenina/genéticaRESUMO
Telomerase is a ribonucleoprotein reverse transcriptase that synthesizes and maintains telomeric DNA. Studies of telomeres and telomerase are facilitated by the large number of linear DNA molecules found in ciliated protozoa, such as Tetrahymena thermophila. To examine the expression of telomerase, we investigated the transcription of the RNA polymerase III-directed gene encoding the RNA subunit (TER1) of this enzyme. A chimeric gene containing the Glaucoma chattoni TER1 transcribed region flanked by 5' and 3' Tetrahymena regions was used to identify promoter elements following transformation of Tetrahymena cells. Disruption of a conserved proximal sequence element (PSE) located at -55 in the Tetrahymena TER1 5' flanking region eliminated expression of the chimeric gene. In addition, mutation of an A/T-rich element at -25 decreased expression markedly. A gel mobility shift assay and protein-DNA cross-linking identified a PSE-binding polypeptide of 50-60 kDa in Tetrahymena extracts. Gel filtration analysis revealed a native molecular mass of approximately 160 kDa for this binding activity. Our results point to a similar architecture between ciliate telomerase RNA and metazoan U6 small nuclear RNA promoters.
