Words similar to tetrahymena
Example sentences for: tetrahymena
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Tetrahymena telomerase and the binder/cutter appear to act concertedly in vivo , as if in a physical complex [ 48 49 ] . However, this contrasts with in vitro properties of the enzyme from exconjugants: 1.) it acts on non-telomeric primers [ 44 50 ] , and 2.) it apparently is no larger than the vegetative enzyme [ 44 ] . Furthermore, telomerase can act in the vegetative MAC of Paramecium , uncoupled from chromatid breakage [ 51 ] . It remains to be seen if a complex between telomerase and binder/cutter activity does exist.
However, the ciliate literature is unclear about whether Tetrahymena telomerase might be able to act uncoupled from the action of the binder/cutter (see Introduction).
Although chromatid breakage requires an endonuclease activity, the cutter, directed by a Cbs-binding activity, no Cbs-dependent "binder/cutter" activity has been detected in vitro . The cutter could be an activity of telomerase itself [ 39 43 ] . Telomerase of both Tetrahymena and Euplotes has a single-strand endonuclease activity [ 45 43 ] . It can trim potential primers back, so that the 3' terminus pairs with template RNA [ 46 ] . Thus, while it may serve a 3' editing function, the existence of a nuclease activity in potential proximity to the site of chromatid breakage is provocative, suggesting that telomerase provides the
The exact nucleotide positions where telomere repeats are added have been examined in several ciliates (reviewed by [ 23 53 ] ). Cloned chromosome ends from 81 MAC family indicated heterogeneity of TAS placement, which we attributed to exonuclease erosion of the broken ends prior to telomerase action [ 27 ] . Analogous multi-TAS regions have been described in Tetrahymena ( [ 49 ] ; E. Hamilton and E. Orias, pers.
A short 15 bp cis -acting sequence, cbs, is necessary and sufficient to direct breakage at or near it in Tetrahymena , presumably being the binding site of the breakage enzyme - the "cutter" [ 34 35 36 ] . The cbs sits in eliminated sequence, a short, variable distance from the positions that receive telomeres.
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