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Molecular and Cellular Biology, January 2001, p. 126-135, Vol. 21, No. 1
Verna and Marrs McLean Department of
Biochemistry and Molecular Biology,1
Cell and Molecular Biology Program,2 and
Department of Molecular and Human
Genetics,3 Baylor College of Medicine, Houston,
Texas 77030
Received 15 August 2000/Returned for modification 19 September
2000/Accepted 3 October 2000
Telomere repeat sequences cap the ends of eucaryotic chromosomes
and help stabilize them. At interstitial sites, however, they may
destabilize chromosomes, as suggested by cytogenetic studies in
mammalian cells that correlate interstitial telomere sequence with
sites of spontaneous and radiation-induced chromosome rearrangements.
In no instance is the length, purity, or orientation of the telomere
repeats at these potentially destabilizing interstitial sites known. To
determine the effects of a defined interstitial telomere sequence on
chromosome instability, as well as other aspects of DNA metabolism, we
deposited 800 bp of the functional vertebrate telomere repeat,
TTAGGG, in two orientations in the second intron of the
adenosine phosphoribosyltransferase (APRT) gene in Chinese
hamster ovary cells. In one orientation, the deposited telomere
sequence did not interfere with expression of the APRT gene, whereas in the other it reduced mRNA levels slightly. The telomere sequence did not induce chromosome truncation and the seeding
of a new telomere at a frequency above the limits of detection. Similarly, the telomere sequence did not alter the rate or distribution of homologous recombination events. The interstitial telomere repeat
sequence in both orientations, however, dramatically increased gene
rearrangements some 30-fold. Analysis of individual rearrangements confirmed the involvement of the telomere sequence. These studies define the telomere repeat sequence as a destabilizing element in the
interior of chromosomes in mammalian cells.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.1.126-135.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Insertion of a Telomere Repeat Sequence into a
Mammalian Gene Causes Chromosome Instability

and
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular Biology, Baylor College of Medicine, One
Baylor Plaza, Houston, TX 77030. Phone: (713) 798-5760. Fax: (713)
796-9438. E-mail: jwilson{at}bcm.tmc.edu.
Present address: Office of Technology and Licensing, University of
Texas, Austin, TX 78759.
Present address: Pangene Corporation, Mountain View, CA 94043.
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