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Molecular and Cellular Biology, June 2000, p. 4128-4134, Vol. 20, No. 11
Department of Biology, University of
Rochester, Rochester, New York 14627
Received 1 December 1999/Returned for modification 3 January
2000/Accepted 3 March 2000
Conversion of the germ line micronuclear genome into the genome of
a somatic macronucleus in Tetrahymena thermophila requires several DNA rearrangement processes. These include (i) excision and
subsequent elimination of several thousand internal eliminated sequences (IESs) scattered throughout the micronuclear genome and (ii)
breakage of the micronuclear chromosomes into hundreds of DNA
fragments, followed by de novo telomere addition to their ends.
Chromosome breakage sequences (Cbs) that determine the sites of
breakage and short regions of DNA adjacent to them are also eliminated.
Both processes occur concomitantly in the developing macronucleus. Two
stage-specific protein factors involved in germ line DNA elimination
have been described previously. Pdd1p and Pdd2p (for programmed DNA
degradation) physically associate with internal eliminated sequences in
transient electron-dense structures in the developing macronucleus.
Here, we report the purification, sequence analysis, and
characterization of Pdd3p, a novel developmentally regulated,
chromodomain-containing polypeptide. Pdd3p colocalizes with Pdd1p in
the peripheral regions of DNA elimination structures, but is also found
more internally. DNA cross-linked and immunoprecipitated with Pdd1p- or
Pdd3p-specific antibodies is enriched in IESs, but not Cbs, suggesting
that different protein factors are involved in elimination of these two
groups of sequences.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
A Novel Chromodomain Protein, Pdd3p, Associates
with Internal Eliminated Sequences during Macronuclear Development in
Tetrahymena thermophila

*
Corresponding author. Present address: Department of
Biochemistry and Molecular Genetics, University of Virginia,
Charlottesville, VA 22908. Phone: (804) 243-6048. Fax: (804) 924-5069. E-mail: allis{at}virginia.edu.
Present address: Department of Molecular Biology, Lewis Thomas Lab,
Princeton University, Princeton, NJ 08544.
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