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Molecular and Cellular Biology, August 1999, p. 5631-5641, Vol. 19, No. 8
Division of Basic Sciences, Fred Hutchinson
Cancer Research Center, Seattle, Washington 98109
Received 23 February 1999/Returned for modification 9 April
1999/Accepted 11 May 1999
In the ciliate Tetrahymena thermophila, thousands of
DNA segments of variable size are eliminated from the developing
somatic macronucleus by specific DNA rearrangements. It is unclear
whether rearrangement of the many different DNA elements occurs via a single mechanism or via multiple rearrangement systems. In this study,
we characterized in vivo cis-acting sequences required for
the rearrangement of the 1.1-kbp R deletion element. We found that
rearrangement requires specific sequences flanking each side of the
deletion element. The required sequences on the left side appear to
span roughly a 70-bp region that is located at least 30 bp from the
rearrangement boundary. When we moved the location of the left
cis-acting sequences closer to the eliminated region, we
observed a rightward shift of the rearrangement boundary such that the
newly formed deletion junction retained its original distance from this
flanking region. Likewise, when we moved the flanking region as much as
500 bp away from the deletion element, the rearrangement boundary
shifted to remain in relative juxtaposition. Clusters of base
substitutions made throughout this critical flanking region did not
affect rearrangement efficiency or accuracy, which suggests a complex
nature for this regulatory sequence. We also found that the right
flanking region effectively replaced the essential sequences identified
on the left side, and thus, the two flanking regions contain sequences
of analogous function despite the lack of obvious sequence identity.
These data taken together indicate that the R-element flanking regions
contain sequences that position the rearrangement boundaries from a
short distance away. Previously, a 10-bp polypurine tract flanking the
M-deletion element was demonstrated to act from a distance to determine
its rearrangement boundaries. No apparent sequence similarity exists between the M and R elements. The functional similarity between these
different cis-acting sequences of the two elements is firm support for a common mechanism controlling Tetrahymena rearrangement.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Flanking Regulatory Sequences of the
Tetrahymena R Deletion Element Determine the Boundaries of
DNA Rearrangement

and
*
Corresponding author. Mailing address: Division of
Basic Sciences, Fred Hutchinson Cancer Research Center, Mail-stop
A2-168, 1100 Fairview Ave. N., Seattle, WA 98109. Phone: (206)
667-4435. Fax: (206) 667-6526. E-mail:
dchalker{at}fred.fhcrc.org.
Present address: Biology, University of Camerino, Camerino 62032, Italy.
Present address: Department of Biochemistry and Molecular
Biophysics, Columbia University, New York, NY 10032.
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