Phosphohistidine is found in basic nuclear proteins of Physarum polycephalum

Nuclear extracts of the true slime mold, Physarum polycephalum, show protein histidine kinase activity towards exogenous histones [(1985) J. Biol. Chem. 260, 16106–16113]. Physarum microplasmodia were labeled with [ 32P]phosphate in vivo and two basic proteins containing alkali-stable phosphate were detected. The labeled proteins comigrated with Physarum histones H1 (approximately) and H2A and phosphoamino acid analysis showed that each protein contained [ 32P]phosphohistidine. The H2A-like protein was also labeled in isolated nuclei incubated with [ 35S]thio-ATP. We conclude that some Physarum nuclear proteins contain phosphohistidine.