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Reconstitution of Arabidopsis Casein Kinase II from Recombinant Subunits and Phosphorylation of Transcription Factor GBF1

Leszek J. Klimczak, Margaret A. Collinge, Donatella Farini, Giovanni Giuliano, John C. Walker and Anthony R. Cashmore
The Plant Cell
Vol. 7, No. 1 (Jan., 1995), pp. 105-115
DOI: 10.2307/3869841
Stable URL: http://www.jstor.org/stable/3869841
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Reconstitution of Arabidopsis Casein Kinase II from Recombinant Subunits and Phosphorylation of Transcription Factor GBF1
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Abstract

In contrast to the well-defined tetrameric structure of animal and yeast casein kinase II (CKII), plant CKII is found in two forms: a monomeric form and an oligomeric form whose subunit composition is not well defined. The Arabidopsis homologs of the catalytic subunit α (CKA1) and the regulatory subunit β (CKB1) of CKII were expressed in Escherichia coli to examine their ability to form complexes, the effect of CKB1 on the catalytic activity, and the relationship of the recombinant enzymes to those isolated from plant material. Both subunits were found mainly in the inclusion body fraction in the bacterial expression strains, and they were solubilized and renatured with the recovery of catalytic (CKA1) and stimulatory (CKB1) activities. The combination of purified CKA1 and CKB1 proteins resulted in up to 100-fold stimulation of casein kinase activity compared with the CKA1 activity alone, showing that CKB1 has biochemical properties similar to those of the β subunit from animals. CKA1 and CKB1 spontaneously assembled into a tetrameric complex, ${\rm CKA}1_{2}{\rm CKB}1_{2}$, which had properties very similar to those of the oligomeric CKII form isolated from broccoli. However, the properties of the catalytic subunit CKA1 alone differed from those of the broccoli monomeric form of CKII-like activity. Phosphorylation of transcription factor GBF1 with the reconstituted ${\rm CKA}1_{2}{\rm CKB}1_{2}$ enzyme resulted in stimulation of its DNA binding activity and retardation of the protein-DNA complex; these results are identical to those obtained previously with isolated nuclear CKII from broccoli.

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