COP9 Constitutive Photomorphogenic Homolog Subunit 3 (COPS3)

COPS3 possesses kinase activity that phosphorylates regulators involved in signal transduction. It phosphorylates I-kappa-B-alpha, p105, and c-Jun. It acts as a docking site for complex-mediated phosphorylation. The gene is located within the Smith-Magenis syndrome region on chromosome 17.Sequence analysis predicted that COPS3 is a 403-amino acid protein which contains regions with homology to the 26S proteasome S3 regulatory subunit. Autoradiographic analysis showed that the complex phosphorylates JUN, IKBA, and the C-terminal part of the p105 precursor of NFKB. The 26S proteasome is not a phosphorylation target, although immunofluorescence microscopy demonstrated that the 450-kD complex has a cytosolic localization, concentrated around the nucleus.