The human double-stranded DNA-activated protein kinase phosphorylates the 90-kDa heat-shock protein, hsp90 alpha at two NH2-terminal threonine residues.

The 90-kDa heat-shock protein, hsp90, is an abundant cytoplasmic protein that can be phosphorylated in vitro by a double-stranded (ds) DNA-activated protein kinase found in cells from several species. Here we show that the dsDNA-activated protein kinase from human HeLa cells phosphorylates 2 threonine residues in the sequence PEETQTQDQPME at the amino terminus of human hsp90 alpha. Hsp90 beta, which is 97% identical to hsp90 alpha but lacks both amino-terminal threonines, is not phosphorylated by the dsDNA-activated protein kinase. Mouse hsp86 and rabbit hsp90 alpha are homologous to human hsp90 alpha; both heterologous proteins are phosphorylated at the same amino-terminal threonines by the human dsDNA-activated protein kinase.