CNSK1A1 (CK1 alpha 1) is a member of the casein kinase I (CKI) gene family, which encodes serine⁄threonine kinases that preferentially phosphorylate acidic substrates. CKI proteins are monomeric, ranging from 25 to 55 kD, and are found in the nuclei, cytoplasm, and membrane fractions of eukaryotic cells.