Histone H1 is phosphorylated in non-replicating and infective forms of Trypanosoma cruzi

The nuclear structure changes during the differentiation from growing to infective stages of Trypanosoma cruzi. As histone modifications have been correlated with structural and functional changes of chromatin, we investigated whether histones in T. cruzi are modified during the life cycle of this protozoan parasite. We found that histone H1 isolated from proliferating forms (epimastigotes) and from differentiated/infective forms (trypomastigotes) have a distinct migrating pattern in Triton-acetic acid-urea gel electrophoresis. While epimastigotes contain predominantly a fast migrating form, a slow migrating band is prominent in trypomastigotes. By metabolically labeling the cells with radioactive phosphate, we demonstrated that the slow migrating histone H1 band is phosphorylated, and that after alkaline phosphatase treatment, it migrates as the fast form. Parasites arrested at the onset of the S phase of the cell cycle with hydroxyurea (HU) also predominantly have the phosphorylated form of histone H1, suggesting that phosphorylation occurs in non-replicating stages of T. cruzi. We also found that the phosphorylated histone H1 is more weakly associated with the chromatin, being preferentially released at 150 mM NaCl. Therefore, histone H1 phosphorylation varies during the life cycle of T. cruzi, and might be related to changes in the chromatin structure.