pCMB treatment reveals the essential role of cysteinyl residues in conferring functional competence to the regulatory subunit of protein kinase CK2

To assess the functional role of the four conserved cysteinyl residues in t he regulatory beta-subunit of protein kinase CK2, the effect of pCMB and ot her reagents of sulfhydryl groups has been investigated. The pCMB-treated b eta-subunit has lost its ability to form either homodimers or regular alpha (2)beta(2) heterotetramers with the catalytic subunit. It also fails to inc rease catalytic activity toward peptide substrates and to mediate the stimu latory effect of polylysine, The pCMB-treated beta-subunit, however, is sti ll able to prevent calmodulin phosphorylation and to physically interact wi th the alpha-subunit to form inactive complexes whose sedimentation coeffic ient is lower than that of CK2 holoenzyme, These inactive complexes upon tr eatment with reducing agents like DTT are converted into a fully active het erotetrameric holoenzyme. (C) 2000 Academic Press.