Mitotic stability of truncated chromosomes assessed by hybridization with plasmid DNA. Expansion of the locus encompassing the strand-switch domain shows the GC-rich (filled box) and coding (hatched boxes) regions. Green arrows identify ORFs (confirmed and potential) and point in the direction of polycistronic transcription. The sites of integration-mediated chromosome fragmentation (1-8) are shown with arrowheads representing the new telomeres. This numbering system is unrelated to that in Figure 4. (Black) Mitotically stable truncated chromosomes; (blue) mitotically unstable; (red) integration not achievable. Transfected clones were grown in the absence of G418 for the generations indicated above the corresponding track. Genomic DNA was probed with plasmid DNA (autoradiographs 1-8), then rehybridized with β-tubulin to control for loading.