CK2 is a pleiotropic and constitutively active serine/threonine protein kinase composed of two catalytic (α and/or α′) and two regulatory β-subunits, whose mechanism of modulation is still obscure. Here we show that CK2 α/α′ subunits undergo intermolecular (trans) tyrosine-autophosphorylation, which is dependent on intrinsic catalytic activity and is suppressed by the individual mutation of Tyr182, a crucial residue of the activation loop, to phenylalanine. At variance with serine-autophosphorylation, tyrosine-autophosphorylation of CK2α is reversed by ADP and GDP and is counteracted by the β-subunit and by a peptide reproducing the activation loop of CK2α/α′ (amino acids 175–201). These results disclose new perspectives about the mode of regulation of CK2 catalytic subunits.

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