Rpn9p

Rpn9p, or regulatory particle non-ATPase subunit 9, is a proteasomal subunit found in eukaryotic cells. In Saccharomyces cerevisiae, the protein is encoded by the RPN9 gene.

Rpn9p is a non-ATPase component of the 19S regulatory particle that associates with the 20S core particle to constitute the 26S proteasome. It is believed to contribute to the proper assembly and stability of the regulatory particle and to the processing of ubiquitinated substrates, including recognition, unfolding, and translocation into the core particle.

In yeast and other eukaryotes, Rpn9p interacts with other regulatory particle subunits and assembly factors; its function is necessary for efficient proteasome-mediated degradation. Localization is typically cytoplasmic and nuclear, reflecting the distribution of the proteasome in the cell.

Genetic disruption of RPN9 can lead to defects in proteasome function and growth phenotypes, particularly under stress or proteotoxic conditions. Evolutionarily, Rpn9p belongs to a family of conserved 19S subunits; homologous proteins exist in a wide range of eukaryotes, indicating a conserved role in proteasome regulation.