Cloning and characterization of the cDNA coding for the catalytic alpha subunit of CK2 from tobacco

We have previously reported the participation of the protein kinase CK2 in the mechanism by which salicylic acid activates transcription of genes, suc h as those coding for glutathion S-transferases, in tobacco. With the purpo se of further studying the participation of CK2 in this signal transduction pathway, we isolated and sequenced the cDNA from the NtCK2A gene, coding f or the catalytic alpha subunit of CK2 from tobacco. The NtCK2A cDNA was iso lated by screening of a tobacco cDNA library with a heterologous probe from Arabidopsis thaliana, followed by 3'RACE to obtain the 3' region. Sequence analysis of the NtCK2A cDNA showed a high level of identity between this C K2 alpha protein sequence and the corresponding sequences of other plant sp ecies such as Arabidopsis and maize (92-95% identity), or those of animal s pecies such as human and Xenopus laevis (75% identity). The expression of t he NtCK2A gene in different tissues from tobacco plants was analyzed by Nor thern blot. High levels of expression of this gene were observed in prolife rating tissues such as shoot and root apical meristems. A recombinant CK2 a lpha protein was obtained after expression of the NtCK2A cDNA in Escherichi a coli. The ability of this recombinant CK2 alpha subunit to phosphorylate casein was inhibited by heparin and stimulated by the CK2 beta subunit from Xenopus laevis.