Not4‐dependent translational repression is important for cellular protein homeostasis in yeast

Abstract

Translation of aberrant or problematic mRNAs can cause ribosome stalling which leads to the production of truncated or defective proteins. Therefore, cells evolved cotranslational quality control mechanisms that eliminate these transcripts and target arrested nascent polypeptides for proteasomal degradation. Here we show that Not4, which is part of the multifunctional Ccr4-Not complex in yeast, associates with polysomes and contributes to the negative regulation of protein synthesis. Not4 is involved in translational repression of transcripts that cause transient ribosome stalling. The absence of Not4 affected global translational repression upon nutrient withdrawal, enhanced the expression of arrested nascent polypeptides and caused constitutive protein folding stress and aggregation. Similar defects were observed in cells with impaired mRNA decapping protein function and in cells lacking the mRNA decapping activator and translational repressor Dhh1. The results suggest a role for Not4 together with components of the decapping machinery in the regulation of protein expression on the mRNA level and emphasize the importance of translational repression for the maintenance of proteome integrity.

The Ccr4-Not complex monitors the translating ribosome for codon optimality

“…Since non-optimal codons affect the decoding kinetics and mRNA degradation occurs co-translationally, it is expected that codon optimality is directly monitored on the ribosome. A physical link of the Ccr4-Not complex to the ribosome has been suggested previously, in particular to polyribosomes (9,10). The Not4 subunit of the complex, an E3-ligase, ubiquitinates proteins of the 40S small ribosomal subunit (11,12), and the Not5 subunit appears to be important for mRNA translatability and polyribosome levels in yeast (13).…”

ATPase activity of the DEAD-box protein Dhh1 controls processing body formation

“…Interestingly, there is increasing evidence that the CCR4-NOT complex functions at several other steps during gene expression outside of mRNA decay, including transcription (Gupta et al, 2016; Kruk et al, 2011; Villanyi and Collart, 2015) and translation (Panasenko, 2014; Preissler et al, 2015). Future work is needed to address how the activity of this multifunctional protein complex is modulated in order to regulate and coordinate multiple steps of gene expression.…”

Translational Capacity of a Cell Is Determined during Transcription Elongation via the Ccr4-Not Complex

“…Recently, we have shown that Not5 plays a role in translatability and assembly of the RNAPII complex (Villanyi et al, 2014). In addition, components of the Ccr4-Not complex, particularly Not4 and Not5, are important for transcription elongation (Kruk et al, 2011) and protein quality control (Dimitrova et al, 2009; Halter et al, 2014; Preissler et al, 2015). Hence these components of the Ccr4-Not complex are prime candidates to coordinate transcription with translation.…”