T. brucei (a) minichromosomes and (b) intermediate chromosomes are resistant to etoposide-mediated cleavage. (a) Procyclics (927 strain) were treated with 500 μM etoposide for 3 h and chromosomal DNA separated by CHEFE. Southern blots were hybridized with the 177 bp repeat probe or α-tubulin. (b) Bloodstream form T. brucei (427 strain) were treated with 25 μM etoposide for 1 h and chromosomal DNA analyzed as above. Blots were hybridized with the intermediate chromosome-specific probe T3. In strain 427, chromosome 1 is larger than in strain 927, as is the major cleavage product identified with the α-tubulin probe. Lane N, non-treated parasites; lane E, etoposide-treated.