AbstractThe Ccr4–Not complex is a conserved multi protein complex with diverse roles in the mRNA life cycle. Recently we determined that the Not1 and Not4 subunits of Ccr4–Not inversely regulate mRNA solubility and thereby impact dynamics of co-translation events. One mRNA whose solubility is limited by Not4 isMMF1encoding a mitochondrial matrix protein. In this work we uncover a mechanism that limitsMMF1overexpression and depends upon its co-translational targeting to the mitochondria. We have named this mechanism Mito-ENCay. This mechanism relies on Not4 promoting ribosome pausing duringMMF1translation, and hence the co-translational docking of theMMF1mRNA to mitochondria via the mitochondrial targeting sequence of the Mmf1 nascent chain, the Egd1 chaperone, the Om14 mitochondrial outer membrane protein and the co-translational import machinery. Besides co-translationalMitochondrial targeting, Mito-ENCay depends uponEgd1 ubiquitination byNot4, theCaf130 subunit of the Ccr4–Not complex, the mitochondrial outer membrane proteinCis1,autophagy and no-go-decay.