Nucleic Acids Research, 2002, Vol. 30, No. 12 2639-2646
© 2002 Oxford University Press
Gene rearrangements induced by the DNA double-strand cleaving agent neocarzinostatin: conservative non-homologous reciprocal exchanges in an otherwise stable genome
Department of Pharmacology and Toxicology and 1Department of Human Genetics, Virginia Commonwealth University, Richmond, VA 23298, USA
Among a collection of 74 aprt mutations induced by treatment of plateau phase Chinese hamster ovary CHO cells with the radiomimetic DNA double-strand cleaving agent neocarzinostatin, nine were large-scale rearrangements. Molecular analysis indicated that all nine were highly conservative, non-homologous reciprocal exchanges, most of which were intrachromosomal as determined by fluorescence in situ hybridization. All but one of the parental sequences contained potential double-strand cleavage sites positioned such that the observed rearrangements could be explained by drug-induced double-strand breakage followed by trimming, templated patching and ligation of the exchanged ends. Predicted non-complementary 3' overhangs were often preserved in the newly formed junctions, suggesting alignment-based fill-in of the overhangs. Banding of metaphase spreads of these mutants, and of a number of mutants induced by the functionally similar compound bleomycin, revealed that bleomycin-induced reciprocal exchange mutants had multiple additional chromosome alterations and considerable chromosomal heterogeneity within each mutant line. In contrast, neocarzinostatin-induced reciprocal exchange mutants, as well as bleomycin-induced base substitution and single base deletion mutants, retained stable pseudodiploid karyotypes similar to that of the parent line. Thus, some reciprocal exchanges arising from misjoining of double-strand breaks were associated with global chromosomal instability, while other ostensibly similar events were not.
* To whom correspondence should be addressed at: Virginia Commonwealth University, PO Box 980230, Richmond, VA 23298-0230, USA. Tel: +1 804 828 9640; Fax: +1 804 828 8079; Email: lpovirk{at}hsc.vcu.edu
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