RESUMEN
The human histones H1 zero and H1.2 were expressed in E. coli and purified to homogenity. Their cytotoxicity on the human leukemia cell line K562 and on PBMC from healthy volunteers was compared with the cytotoxic effect of a bovine histone H1 preparation. In this preparation, histone H1.2 was identified as the main compound. All three histone preparations induced a significant dose-dependent toxicity on the leukemia cell line. Compared with the recombinant histone H1 zero, the bovine preparation and recombinant H1.2 showed stronger cytotoxicities. Cytotoxic effects on K562 cells were observed immediately after addition of the histones, whereas the histone preparations failed to induce significant cytotoxicity on PBMC during the first hour of incubation. However, after 24 hours all three histone preparations induced toxic effects on PBMC which were comparable to those observed on the leukemia cell line.