Article

Molecular and Cellular Biochemistry

, Volume 129, Issue 1, pp 77-85

A majority of casein kinase II α subunit is tightly bound to intranuclear components but not to the β subunit

  • J. StigareAffiliated withDepartment of Cell and Molecular Biology, Medical Nobel Institute, Laboratory of Medical Cell Biology, Karolinska Institutet
  • , N. BuddelmeijerAffiliated withDepartment of Cell and Molecular Biology, Medical Nobel Institute, Laboratory of Medical Cell Biology, Karolinska Institutet
  • , A. PigonAffiliated withDepartment of Cell and Molecular Biology, Medical Nobel Institute, Laboratory of Medical Cell Biology, Karolinska Institutet
  • , E. EgyhaziAffiliated withDepartment of Cell and Molecular Biology, Medical Nobel Institute, Laboratory of Medical Cell Biology, Karolinska Institutet

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Abstract

Nuclear casein kinase II (CK II) was purified from an epithelial cell line ofChironomus tentans and characterized. The intracellular distribution of CK II and its two intracellular subunits (α and β) was analysed by immunoblotting. The apparent molecular weights of the α and β subunits were estimated to be 36 and 28 kDa, respectively. Like other purified CK II preparations, CK II fromChironomus tentans is able to use ATP or GTP for phosphorylation of casein and phosvitin, and its activity is strongly inhibited by heparin and by the transcription inhibitor 5,6-dichloro-1-β-D-ribofuranosylbenzimidazole (DRB). Due to their differential solubilities in NaCl and (NH4)2SO4 solutions, individual α and β subunit pools could be detected. More than 85% of the total immunostainable α subunit and essentially all immunoreactive individual β subunit and heterooligomeric enzyme molecules were localised to the nucleus. Unexpectedly, more than 80% of this nuclear α subunit was insoluble in 0.35 M NaCl, while all individual β subunit and heterooligomeric enzyme molecules were solubilized under the same conditions. Of the 0.35 M NaCl soluble kinase fractions, the active multisubunit form of CK II precipitated in 50% (NH4)2SO4 and could thus be separated from the free β subunit, which precipitated at 60% and 80% (NH4)2SO4. These results suggest that a major portion of the nuclear CK II α subunit does not form heterooligomeric structures with the β subunit, but binds tightly to nuclear components.

Key words

protein phosphorylation casein kinase II subunit distribution inhibitior DRB heparin