Etoposide-mediated cleavage sites in T. cruzi chromosome 3. Epimastigotes were treated with 1 mM etoposide for 6 h and chromosomal DNA fractionated by CHEFE and assessed by Southern analysis. Probe Tc12 is specific to the larger homologue (see Materials and methods). Lane N, non-treated parasites; lane E, etoposide-treated. The schematic shows both chromosome 3 homologues, location of the 16 kb GC-rich strand-switch domain (GC), positions of the probes and predicted locations of the major Topo-II cleavage sites (large black arrowheads). The fragments generated (1-7), and their sizes and inferred positions on the chromosomes are shown in red, green and blue. With the exception of probe Tc12, fragments derived from the right arm of the 1.1 Mb homologue (blue) cannot be detected, due to co-migration with the cross-hybridizing 0.65 Mb homologue.