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 (PubMed:17310242, PubMed:19414601). 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 (PubMed:25862660). Interacts with CLOCK. Forms a ternary complex with the CLOCK-ARNTL/BMAL1 heterodimer. 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. Expressed in the heart, kidney and liver and shows a circadian oscillation in these tissues with a peak at circadian time 14 hours (at protein level). Expressed in the brain, including the suprachiasmatic nucleus (SCN) of the brain, and in multiple peripheral tissues such as heart, liver and kidney. Exhibits a circadian oscillation in the peripheral tissues with a peak at circadian time 14 hours. No visible phenotype. Knockout mice display normal locomotor activity rhythms and normal behavioral responses to light. Animals show reduction liver PER1 peak levels, but no change in the expression of other core clock genes. It is uncertain whether Met-1 or Met-36 is the initiator. Extended N-terminus.