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ABSTRACT TARGETED recombination in mammalian cells is rare compared with non-homologous integration1–5. In _Saccharomyces cerevisiae_ the reverse is true6,7. Differences in tageting
efficiency could arise because a target of unique DNA is 200 times more dilute in mammalian genomes than it is in yeast. We tested this possibility by measuring gene targeting in normal CHO
cells with two copies of the dihydrofolate reductase (DHFR) gene and in amplified CHOC 400 cells, which carry 800 copies8. If the concentration of the target gene is critical, amplified
cells should show an enhanced frequency of targeted recombination relative to non-homologous integration. Using a positive/negative selection protocol3, we demonstrated that the efficiency
of targeting into DHFR genes is indistinguishable in normal and amplified CHO cells. As targeting does not depend on the number of targets, the search for homology is not a rate-limiting
step in the mammalian pathway of gene targeting. Thus, the difference in genome size is not the basis for the different outcomes of targeting experiments in _S_. _cerevisiae_ and mammals.
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Article CAS Google Scholar Download references AUTHOR INFORMATION Author notes * John H. Wilson: To whom correspondence should be addressed. AUTHORS AND AFFILIATIONS * Verna and Marrs
McLean Department of Biochemistry, Bay lor College of Medicine, Houston, Texas, 77030, USA Hui Zheng & John H. Wilson Authors * Hui Zheng View author publications You can also search for
this author inPubMed Google Scholar * John H. Wilson View author publications You can also search for this author inPubMed Google Scholar RIGHTS AND PERMISSIONS Reprints and permissions
ABOUT THIS ARTICLE CITE THIS ARTICLE Zheng, H., Wilson, J. Gene targeting in normal and amplified cell lines. _Nature_ 344, 170–173 (1990). https://doi.org/10.1038/344170a0 Download citation
* Received: 24 November 1989 * Accepted: 11 January 1990 * Issue Date: 08 March 1990 * DOI: https://doi.org/10.1038/344170a0 SHARE THIS ARTICLE Anyone you share the following link with will
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