Nucleic Acids Research, Vol 26, Issue 17 3998-4004, Copyright © 1998 by Oxford University Press
J Bednenko, M Melek and DE Shippen
Telomerase from the ciliate Euplotes crassus incorporates G4T4telomeric
repeats onto both telomeric and non-telomeric single-stranded DNA 3'- ends
via reverse transcription of a templating domain in its RNA subunit. Here
we describe an unusual mode of template copying that is characteristic of
DNA synthesis onto non-telomeric 3'-ends in vitro . When dTTP was
eliminated from telomerase reactions, telomeric primers or DNA products
generated from the telomerase endonuclease were extended by precise copying
of the RNA template. In contrast, telomerase catalyzed the addition of up
to 13 dG residues onto primers with non-telomeric 3'-ends under the same
reaction conditions. Introducing mismatches in the 3'-terminus of telomeric
primers that reduced primer complementarity to the RNA template induced
reiterative dG incorporation, indicating that the reaction is influenced by
Watson- Crick base pair formation between the primer and the RNA template.
Unexpectedly, the reiterative dG addition mode was confined to telomerase
derived from developing cells that undergo new telomere formation. This
reaction was not observed in vegetatively growing cells. We postulate that
indiscriminate dG addition by telomerase occurs by reiterative copying of C
residues in the telomerase RNA templating domain and reflects lateral
instability of the primer- template interaction during de novo telomere
formation.
ARTICLES
Reiterative dG addition by Euplotes crassus telomerase during extension of non-telomeric DNA
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA.
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