The present invention describes a novel human protein kinase related to citron kinase, and its encoding polynucleotide. Also described are expression vectors, host cells, antisense molecules, and antibodies associated with the protein kinase polynucleotide and/or polypeptide of this invention. In addition, methods for treating, diagnosing, preventing, and screening for disorders or diseases associated with abnormal biological activity of the protein kinase are described, as are methods for screening for modulators, e.g., agonists or antagonists, of the protein kinase activity and/or function.