The function of CNOT4 (CCR4-NOT transcription complex subunit 4, ENSG00000080802) is as follows. Has E3 ubiquitin ligase activity, promoting ubiquitination and degradation of target proteins (PubMed:11823428, PubMed:22159038, PubMed:26575292). Involved in activation of the JAK/STAT pathway (PubMed:11823428, PubMed:22159038). Catalyzes ubiquitination of methylated RBM15 (PubMed:26575292). Plays a role in quality control of translation of mitochondrial outer membrane-localized mRNA (PubMed:29861391). As part of the PINK1-regulated signaling, upon mitochondria damage, ubiquitinates ABCE1 and thereby recruits autophagy receptors to the mitochondrial outer membrane to initiate mitophagy (PubMed:29861391). {ECO:0000269|PubMed:11823428, ECO:0000269|PubMed:22159038, ECO:0000269|PubMed:26575292, ECO:0000269|PubMed:29861391}.