The CCR4-NOT complex is an evolutionarily conserved, multi-component complex known to be involved in transcription as well as mRNA degradation. Various subunits within the complex are involved in influencing nuclear hormone receptor activities. The CCR4-NOT complex is also involved in the regulation of Histone H3 lysine 4 methylation through a ubiquitin-dependent pathway that likely involves the proteasome. CNOT4 (CCR4-NOT transcription complex subunit 4), also known as CCR4-associated factor 4 and E3 ubiquitin-protein ligase CNOT4, is a 575 amino acid protein that is a subunit of the CCR4-NOT complex. CNOT4 contains one C3H1-type zinc finger, one RING-type zinc finger and one RRM (RNA recognition motif) domain. Via its RING domain, CNOT4 binds E2 ubiquitin ligases. CNOT4 functions as a UbcH5B-dependent ubiquitin-protein ligase (E3 ligase). There are eight isoforms of CNOT4 that are expressed as a result of alternative splicing events.