Role of the ribosome‐associated protein PY in the cold‐shock response of E scherichia coli

Abstract

Protein Y ( PY ) is an E scherichia coli cold‐shock protein which has been proposed to be responsible for the repression of bulk protein synthesis during cold adaptation. Here, we present in vivo and in vitro data which clarify the role of PY and its mechanism of action. Deletion of yfiA , the gene encoding protein PY , demonstrates that this protein is dispensable for cold adaptation and is not responsible for the shutdown of bulk protein synthesis at the onset of the stress, although it is able to partially inhibit translation. In vitro assays reveal that the extent of PY inhibition changes with different mRNA s and that this inhibition is related to the capacity of PY of binding 30S subunits with a fairly strong association constant, thus stimulating the formation of 70S monomers. Furthermore, our data provide evidence that PY competes with the other ribosomal ligands for the binding to the 30S subunits. Overall these results suggest an alternative model to explain PY function during cold shock and to reconcile the inhibition caused by PY with the active translation observed for some mRNA s during cold shock. E scherichia coli responds to cold stress by entering an acclimation phase during which protein synthesis slows down considerably with the exception of a specific set of genes (cold‐shock genes) whose expression is stimulated. In this article, we have investigated in vivo and in vitro the role of PY , a protein that is associated with the ribosome throughout the cold acclimation phase. Our data indicate that protein PY can affect translation initiation but is not responsible for turning off bulk protein synthesis during the cold stress.