C1D

C1D Full Name

C1D nuclear receptor corepressor

C1D Introduction

C1D (C1D nuclear receptor corepressor) is a multifunctional nuclear protein that plays critical roles in transcriptional regulation, RNA processing, DNA damage repair, and the induction of apoptosis. The gene encoding C1D is located on human chromosome 2p14 and produces a small protein of approximately 141 amino acids with a molecular weight of about 16 kDa. C1D is evolutionarily well conserved, with orthologs identified across diverse species from yeast to humans, and its yeast homologue is known as Rrp47. The protein is ubiquitously expressed in virtually all human tissues, with particularly high levels detected in the hippocampus, medulla oblongata, mammary gland, thyroid and salivary gland, as well as in fetal lung, liver and kidney. C1D was originally identified as a DNA-binding and apoptosis-inducing protein that localizes to the nucleus, where it exerts its diverse biological functions.

Figure 1.C1D gene and function overview.

Structural Domains and Biochemical Properties
C1D is a relatively small but highly versatile protein that can exist as both a monomer and a homodimer in its functional state. The three-dimensional structure of C1D has not been fully resolved, but biochemical characterization has revealed that it possesses high-affinity DNA-binding activity, enabling it to interact directly with double-stranded DNA. The protein is predominantly localized to the nucleus, specifically within the nucleolus and nucleoplasm, consistent with its roles in RNA processing and chromatin organization. C1D lacks classical enzymatic domains but contains regions that mediate interactions with multiple protein partners, including the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), the RNA exosome component EXOSC10, and the TRAX/Translin complex. The protein is also subject to post-translational modifications, including phosphorylation by DNA-PK, which may regulate its activity and interactions. Multiple transcript variants of C1D exist, but they encode the same protein, and several pseudogenes of this gene have been identified on chromosome 10.

DNA Damage Repair and Genomic Stability
C1D is a critical player in the maintenance of genomic stability through its involvement in the repair of DNA double-strand breaks (DSBs). The protein interacts with and activates the DNA-dependent protein kinase (DNA-PK), a key regulator of the non-homologous end joining (NHEJ) pathway. C1D binds to the putative leucine zipper region of the DNA-PK catalytic subunit (DNA-PKcs) and serves as a very effective substrate for DNA-PK phosphorylation. Remarkably, C1D can direct the activation of DNA-PK in a manner that does not require DNA ends, representing a unique mechanism of kinase activation. Studies in Saccharomyces cerevisiae have demonstrated that disruption of the yeast C1D homologue (YC1D) results in defects in both NHEJ and homologous recombination (HR) pathways for DSB repair, indicating that C1D is implicated in both major repair pathways. Researchers have proposed that C1D is situated in a central position to maintain genomic stability at highly transcribed gene loci by coordinating RNA processing and DNA repair through the timely recruitment of relevant regulatory factors.

Alternate Names for C1D

C1D; C1D nuclear receptor corepressor; C1D nuclear receptor co repressor; nuclear nucleic acid-binding protein C1D; LRP1; small unique nuclear receptor co repressor; SUN CoR; SUNCOR; C1D DNA-binding protein; nuclear DNA-binding protein