MOLECULAR-CLONING AND EXPRESSION OF GLYCOGEN-SYNTHASE KINASE-3 FACTOR-A

Glycogen synthase kinase-3 (GSK-3) is a protein-serine kinase implicated in the hormonal control of several regulatory proteins including glycogen synthase and the transcription factor c-jun. Two classes of rat brain cDNA for this enzyme have been isolated termed GSK-3α and GSK-3β. The α-type encodes a 51 kd polypeptide, the sequence of which includes all of the tryptic peptides determined by protein sequence analysis of purified skeletal muscle GSK-3. The novel β-type cDNA has the potential to encode a 47 kd protein with 85% amino acid identity to GSK-3α. The two types of cDNA are the products of distinct genes as determined by genomic organization and nucleic acid sequence analysis. Both α and β clones exhibit kinase activity when expressed in COS-1 cells and type-specific antibodies to GSK-3 α and β detect proteins of 51 and 47 kd, respectively, in a variety of rat tissue extracts, with highest levels of both in brain. Partial purification of GSK-3 activity from bovine brain results in the isolation of active α and β proteins. The physiological importance of these two proteins in cellular signal transduction is discussed.