Indeed, an increased translation rate of S. kudriavzevii was observed after cold shock, suggesting that the efficiency of protein synthesis is an important process for the adaptation of yeast cells to grow at low temperatures.
Many codon optimizing and deoptimizing experiments have used both prokaryotic and eukaryotic translation systems and consistently have suggested an increased translation rate with optimized codon usage and a reduced translation rate with deoptimized codon usage (Haas et al. 1996; Ngumbela et al. 2008; Robinson et al. 1984; Sorensen et al. 1989).
Our finding that the activity of complex IV decreased in MetR cells is in striking contrast to findings by others who demonstrated that lifespan extension in flies under protein restriction was associated with enhanced mitochondrial activity, increased activity of OxPhos complexes I and IV, and an increased translation rate for several complex I and IV subunits (Zid et al., 2009).
The observation that codons translated by common tRNAs are used more frequently than synonymous codons translated by rare tRNAs, and that this usage bias strengthens with gene expression level, is interpreted as a signal of selection to increase translation rate [ 5] and/or accuracy[ 6].
Increased eIF4F activity is thought to increase translation rates since eIF4E is the least abundant translation factor and initiation is generally rate-limiting for translation [8], [9].
Rather, it appears that increased translation rates of the oACHE-S mRNA are responsible for the fact that AChE accumulates to higher levels in the oACHE-S plants.
As rapidly cycling cells require increased translation rates, it was postulated that they might be more sensitive to inhibition of protein synthesis.
As regards the regulation model, up-regulation of enzymes associated with amino acid biosynthesis on NMD inactivation, for example, has been related to a feedback circuit coupling low amino acid levels with inactivation of NMD and hence increased translation rates of mRNAs associated with amino acid biosynthesis [ 10].
Furthermore, we know that protein expression level can be increased by three possible steps by 1) increasing transcription rate, 2) increasing translational rate, or 3) increasing both transcription and translation rate.
Our data shows that increased polysomal occupancy is not necessarily leading to more ribosomes per transcript, suggesting a mechanism of translational induction not solely dependent on increased translation initiation rates.
