Nuclease Bal31 sensitivity of genes h49 andjl8. Agarose blocks containing whole chromosomal T. cruzi DNA were incubated with increasing amounts of exonucleaseBal31 (1–5 units in panel A, and 5–30 units in panel B) during 6 h at 30°C following digestion with SfiI restriction enzyme. DNA restriction fragments were resolved by PFGE and hybridized with probes H49 and JL8, and a T. cruzi telomere sequence.