In vitro phosphorylation of human immunodeficiency virus type 1 Tat protein by protein kinase C: evidence for the phosphorylation of amino acid residue serine-46.

Human immunodeficiency virus type-1 Tat protein is phosphorylated by protein kinase C in a calcium-, diacylglycerol-, and phosphatidylserine-dependent manner. Maximum phosphorylation is reached at a stoichiometry of between 0.45 and 0.5 mol of phosphate per mol of Tat. Several Tat peptides, containing serine at position 46, are the only ones which are phosphorylated at significant rates. Several other Tat peptides containing potential protein kinase C phosphorylation sites are not phosphorylated.