Sequencing of Full-Length cDNA Encoding the Alpha and Beta Subunits of Human Casein Kinase II From Human Platelets and Megakaryocytic Cells. Expression of the Casein Kinase IIalpha Intronless Gene in a Megakaryocytic Cell Line
Casein kinase II (CKII) is a ubiquitous protein kinase composed of two subunits, alpha and beta, that can use both ATP and GTP as phosphoryl donors. Two genes located on two separate chromosomes were identified for CKIIalpha: one on chromosome 20 band 13 with an approximate size of 20 kb and a second on chromosome 11 band 15.5-p15.4 that is the same size as the cDNA of locus 20 kb (1.2 kb) and does not contain any introns. The two genes differ in four amino acids. Recently, it has been demonstrated that a membrane-associated platelet-derived CKII phosphorylates coagulation factor Va. The mRNA encoding the platelet CKII was isolated from fresh human platelets, and the corresponding cDNAs encoding the alpha and beta subunits of human platelet CKII were produced and sequenced. The cDNA for platelet CKIIalpha was found to be 99.7% homologous to the CKIIalpha intronless gene, having the same characteristic amino acid residues at positions 128, 256, 287, and 351. However, the cDNA of platelet CKIIalpha has a different amino acid at position 236 (Arg --> His), which is not found in the intronless gene. The cDNA of the CKIIbeta subunit was completely identical with the sequence of the CKIIbeta subunit isolated from other tissues. Since platelets arise from megakaryocytes, mRNA was isolated from the megakaryocytic cell line MEG-01 and the cDNA for CKIIalpha was cloned and sequenced. The cDNA was found to be identical to the intronless gene found in platelets. We have also investigated the expression of the intronless gene in several other cell lines. Expression of the intronless gene was only found in cell line MEG-01. Our data demonstrate expression of the CKIIalpha intronless gene in megakaryocytes and platelets.