911C

911C is a designation used in molecular biology to refer to the 9-1-1 complex subunit C, a component of the DNA damage response in eukaryotic cells. In humans, the 9-1-1 complex is a heterotrimer composed of subunits RAD9A (subunit C), HUS1, and RAD1, and it plays a key role in sensing DNA damage and replication stress.

The 9-1-1 complex functions as a clamp-like structure that is loaded onto damaged DNA and participates in checkpoint signaling. The C subunit, RAD9A, contributes to proper complex assembly and stability, and it helps recruit and coordinate downstream effectors of the DNA damage response. Through interactions with the ATR-ATRIP signaling axis and other repair factors, the complex promotes phosphorylation events and helps regulate cell cycle progression, thereby maintaining genome integrity.

Localization of the 9-1-1 complex is primarily nuclear, with association to chromatin at sites of damage. Regulation occurs through post-translational modifications and protein-protein interactions that modulate loading, stability, and signaling strength. The activity of the RAD9A-containing subcomplex is important for an adequate cellular response to various forms of DNA damage, including ultraviolet damage and replication-associated lesions.

Clinical and research relevance has centered on the 9-1-1 complex’s contribution to genomic stability. Altered expression or function of RAD9A has been observed in certain cancers, and experimental disruption can increase cellular sensitivity to DNA-damaging agents. Ongoing research investigates the complex’s potential as a biomarker and as a target to enhance cancer therapies that rely on DNA damage.