Modified RING finger, HC subclass (C4C4-type), found in CCR4-NOT transcription complex subunit 4 (NOT4) and similar proteins
NOT4, also known as CCR4-associated factor 4, E3 ubiquitin-protein ligase CNOT4, or potential transcriptional repressor NOT4, is a component of the multifunctional CCR4-NOT complex, a global regulator of RNA polymerase II transcription. It associates with polysomes and contributes to the negative regulation of protein synthesis. NOT4 functions as an E3 ubiquitin-protein ligase that interacts with a specific E2, Ubc4/5 in yeast, and the ortholog UbcH5B in humans, and ubiquitylates a wide range of substrates, including ribosome-associated factors. Thus, it plays a role in cotranslational quality control (QC) through ribosome-associated ubiquitination and degradation of aberrant peptides. NOT4 contains a C4C4-type RING finger motif, whose overall folding is similar to that of the C3HC4-type RING-HC finger, a central RNA recognition motif (RRM), and a C-terminal domain predicted to be unstructured.