Preferential translation of cold-shock mRNAs during cold adaptation

Abstract

Upon temperature downshift below the lower threshold of balanced growth (∼20°C), the Escherichia coli translational apparatus undergoes modifications allowing the selective translation of the transcripts of cold shock-induced genes, while bulk protein synthesis is drastically reduced. Here we were able to reproduce this translational bias in E. coli cell-free extracts prepared at various times during cold adaptation which were found to display different capacities to translate different types of mRNAs as a function of temperature. Several causes were found to contribute to the cold-shock translational bias: Cold-shock mRNAs contain cis-elements, making them intrinsically more prone to being translated in the cold, and they are selective targets for trans-acting factors present in increased amounts in the translational apparatus of cold-shocked cells. CspA was found to be among these trans-acting factors. In addition to inducing a higher level of CspA, cold shock was found to cause a strong (twoto threefold) stoichiometric imbalance of the ratio between initiation factors (IF1, IF2, IF3) and ribosomes without altering the stoichiometric ratio between the factors themselves. The most important sources of cold-shock translational bias is IF3, which strongly and selectively favors translation of cold-shock mRNAs in the cold. IF1 and the RNA chaperone CspA, which stimulate translation preferentially in the cold without mRNA selectivity, can also contribute to the translational bias. Finally, in contrast to a previous claim, translation of cold-shock cspA mRNA in the cold was found to be as sensitive as that of a non-cold-shock mRNA to both chloramphenicol and kanamycin inhibition.

Unique role for translation initiation factor 3 in the light color regulation of photosynthetic gene expression

“…In E. coli, cold shock leads to an increase in IF3 abundance relative to ribosome abundance, leading to the preferential translation of cold-shock mRNAs (37). At low temperature, IF3 increases the binding rate of fMet-tRNA to ribosomes associated with cold-shock mRNA, increases the pool size of 30S subunits, and lowers the fidelity of translation of non-cold-shock mRNAs (38).…”

Cold-stress-induced de novo expression of infC and role of IF3 in cold-shock translational bias

“…The transcript of cspA (cspAmRNA) was selected as a paradigm cold-shock mRNA since it has been demonstrated that it is preferentially and efficiently transcribed and translated following cold shock (Gualerzi et al 2003). On the other hand, the transcript of cspD (cspDmRNA) was selected as a paradigm non-cold-shock mRNA because it is expressed during stationary phase and following glucose starvation (Yamanaka and Inouye 1997) but is poorly translated at low temperature (Giuliodori et al 2004).…”

“…However, after cold stress, the level of the IFs increases in the absence of a corresponding increase of the number of ribosomes, thereby creating an exceptional imbalance in the IFs/ribosome ratio. This seems to be at least one of the causes of the above mentioned cold shock translational bias (Giuliodori et al 2004).…”

“…Cold-shock translational bias, namely, the condition that favors translation at low temperature of cold-shock mRNAs, is one of the main and most characteristic mechanisms by which the cell ensures the selective expression of its cold-shock genes (Brandi et al 1996;Goldenberg et al 1997;Giuliodori et al 2004). Translational bias occurs during the 3-5 h (depending upon the temperature) acclimation phase, which begins after the cold stress and ends when the cells resume slow growth at low temperature.…”

“…Furthermore, IF3, together with IF1, was shown to play a fundamental role in determining the translational bias during cold acclimation (Giuliodori et al 2004), but nothing is known of the molecular mechanism(s) of this activity.…”