The RNA chaperone protein CspA stimulates translation during cold acclimation by promoting the progression of the ribosomes

SUMMARY CspA is an RNA binding protein expressed during cold-shock in Escherichia coli, capable of stimulating translation of several mRNAs – including its own – at low temperature. We used reconstituted translation systems to monitor the effects of CspA on the different steps of the translation process and probing experiments to analyze the interactions with its target mRNAs. We specifically focused on cspA mRNA which adopts a cold-induced secondary structure at temperatures below 20°C and a more closed conformation at 37°C. We show that at low temperature CspA specifically promotes the translation of the mRNA folded in the conformation less accessible to the ribosome (37°C form). CspA interacts with its mRNA without inducing large structural rearrangement, does not bind the ribosomal subunits and is not able to stimulate the formation of the translation initiation complexes. On the other hand, CspA promotes the progression of the ribosomes during translation of its mRNA at low temperature and this stimulation is mRNA structure-dependent. A similar structure-dependent mechanism may be responsible for the CspA- dependent translation stimulation observed with other probed mRNAs, for which the transition to the elongation phase is progressively facilitated during cold acclimation with the accumulation of CspA.