Nucleic Acids Research, Vol 26, Issue 12 2908-2916, Copyright © 1998 by Oxford University Press
L Li, S Lejnine, V Makarov and JP Langmore
Telomeres are essential repetitive sequences at the ends of chromosomes
that prevent chromosome fusion and degradation. We have successfully
recapitulated these two protective functions in vivo and in vitro by
incubating blunt-end DNA constructs having vertebrate telomeric ends in
Xenopus eggs and egg extracts. Constructs with telomeric ends are stable as
linear molecules; constructs with non-telomeric ends undergo intramolecular
fusion. In extracts, 99.8% of the telomeric constructs from 78 to 700 bp in
length are assembled into 'model telomeres' in <5 min and have an
extra-polated half-life of >3.5 years. Non-telomeric constructs
circularize with first order kinetics and a half-life of 4 h. In living
eggs the telomeric constructs are protected from fusion and degradation.
The stability of the telomeric constructs is not due to covalent
processing. Extract can protect approximately 100 pM telomeric ends
(equivalent to 1.7 x 10(7) ends/egg) even in the presence of a 20-fold
excess of double-stranded telomeric DNA, suggesting that protection
requires end-specific factors. Constructs with (TTGGGG) n repeats are
unstable, suggesting that short tracts of this and other telomere-like
sequences found within human telomeres could lead to genome instability if
exposed by partial telomere erosion during aging.
ARTICLES
In vitro and in vivo reconstitution and stability of vertebrate chromosome ends
Biophysics Research Division and Department of Biological Sciences, University of Michigan, Ann Arbor, MI 48109-1055, USA.
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