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Mol. Cell. Biol., 12 1995, 7117-7126, Vol 15, No. 12
DK Butler, LE Yasuda and MC Yao
Large palindromic DNAs are found in a wide variety of eukaryotic cells. In
Tetrahymena thermophila, a large palindrome is formed from a single rRNA
gene (rDNA) during nuclear differentiation. We present evidence that a key
step in the formation of the rDNA palindrome of T. thermophila involves
homologous intramolecular recombination. Heteroduplex micronuclear rDNA
molecules were constructed in vitro and microinjected into developing
macronuclei, where they formed palindromes. Analysis of the resulting
palindromes indicated that both strands of the microinjected rDNA are used
to form the same palindrome. This study, together with a previous study (L.
F. Yasuda and M.-C. Yao, Cell 67:505-516, 1991), is the first to define a
molecular pathway of palindrome formation. The process is initiated by
chromosome breakage at sites flanking the micronuclear rDNA. An
intramolecular recombination reaction, guided by a pair of short inverted
repeats located at the 5' end of the excised rDNA, covalently joins the two
strands of micronuclear rDNA in a giant hairpin molecule. Bidirectional DNA
replication converts the giant hairpin molecule to a palindrome. We suggest
that the general features of this pathway are applicable to palindrome
formation in other cell types.
Copyright © 1995, American Society for Microbiology
An intramolecular recombination mechanism for the formation of the rRNA gene palindrome of Tetrahymena thermophila
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104, USA.
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