Cover: An intrachromosomal rearrangement (#B7A) at the CHO aprt locus formed by misjoining of exchanged DNA double-strand break ends. Sequence analysis revealed a highly conservative non-homologous reciprocal exchange between aprt and an unrelated sequence, with breakpoints corresponding to sites of neocarzinostatin-induced double-strand cleavage. The separation of sequences immediately upstream and downstream of aprt, as revealed by metaphase and interphase fluorescence in situ hybridization, shows that the exchange generated an inversion or rearrangement encompassing at least several hundred kilobases within a localized region of the Z4 chromosome. For further details see Wang et al. in this issue [Nucleic Acids Research (2002) 30, 2639-2646].
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