RBFA, A 30S RIBOSOMAL-BINDING FACTOR, IS A COLD-SHOCK PROTEIN WHOSE ABSENCE TRIGGERS THE COLD-SHOCK RESPONSE

The cold-shock response, characterized by a specific pattern of gene e xpression, is induced upon a downshift in temperature and in the prese nce of inhibitors of ribosomal function, Here, we demonstrate that Rbf A of Escherichia coli, considered to be involved in ribosomal maturati on and/or initiation of translation, is a cold-shock protein, Shifting the rbfA mutant to a lower temperature resulted in a constitutive ind uction of the cold-shock response accompanied by slower growth at low temperatures, while shifting the rbfA mutant that overproduces wild-ty pe RbfA resulted in an increase in total protein synthesis accompanied by faster growth adaptation to the lower temperature, Furthermore, th e cold-shock response was also constitutively induced in a cold-sensit ive 16S rRNA mutant at low temperatures, Accompanying the transient in duction of the cold-shock response, we also report that shifting E. co li from 37 degrees C to 15 degrees C resulted in a temporary inhibitio n of initiation of translation, as evidenced by the transient decrease in polysomes accompanied by the transient increase in 70S monosomes, The accumulative data indicate that the inducing signal for the cold-s hock response is the increase in the level of cold-unadapted non-trans latable ribosomes which are converted to cold-adapted translatable rib osomes by the association of cold-shock proteins such as RbfA. Therefo re, the expression of the cold-shock response, and thus cellular adapt ation to low temperature, is regulated at the level of translation. Th e data also indicate that cold-shock proteins can be translated by rib osomes under conditions that are not translatable for most mRNAs.