Phosphorylation of the Major Heat Shock Protein of Dictyostelium discoideum

The major heat shock protein, hsp 70, of Dictyostelium discoideum was found to be rapidly phosphorylated. Analysis of [35S]methionine- and 32Pi-labeled hsp 70 revealed that two similar but distinct proteins of about 70,000 daltons each are synthesized at a high rate after a heat shock, and that each has a phosphorylated member. The phosphorylation chiefly modifies threonine residues. Rapid turnover of the phosphate group occurs, resulting in a steady-state condition in which only about half of the hsp 70 is phosphorylated at a given time.