COP9 signalosome complex (CSN), a complex involved in various cellular and developmental processes. The CSN complex is an ess ential regulator of the ubiquitin conjugation pathway by mediating the deneddylation of the cullin subunits of SCF-type E3 ligase complexes, leading to decrease the Ubl ligase activity of SCF-type complexes such as SCF, CSA or DDB2. CSN4 gene encodes a component of CSN complex, COP9 signalosome complex subunit 4 (COPS4). The ubiquitin-proteasome system plays a major role in the rhythmic accumulation and turnover of molecular clock components. A recent study in Drosophila indicates that CSN lie in a common pathway leading to light-dependent degradation of clock protein Timeless (TIM).