Transcriptional repressor which may act as a negative-feedback regulator of CLOCK-ARNTL/BMAL1 transcriptional activity in the circadian-clock mechanism. May stimulate ARNTL/BMAL1-dependent phosphorylation of CLOCK. However, the physiogical relevance of these observations is unsure, since experiments in knockout mice showed that CIPC is not critially required for basic circadian clock. Interacts with CLOCK. Forms a ternary complex with the CLOCK-ARNTL/BMAL1 heterodimer (By similarity). Interacts with CAD AND HSPA5 (By similarity). Predominantly localizes to the nucleus, where it co-localizes with CLOCK. At the G1/S boundary, partially translocated to the cytosol.