S1 ribosomal protein and the interplay between translation and mRNA decay

In bacteria, transcription, translation and mRNA decay are tightly interconnected processes; however, little is known about specific factors and molecular mechanisms involved in their co-ordination. The ribosomal protein S1, an “atypical” ribosomal protein weakly associated with the 30S subunit of Escherichia coli ribosome, has been implicated in translation, transcription and control of RNA stability. It is thus a good candidate for playing a role in the interplay among these processes. We have addressed S1 function by assaying translation and decay of model full-length and leaderless mRNAs upon modulation of S1 intracellular concentration (from depletion to overexpression). We have shown that S1 over-expression leads to polysome disappearance and translation inhibition. Moreover, in the same condition, RNase E-dependent decay of both the cspE+ and leaderless ΔL-cspE mRNAs is prevented. Conversely, cleavage of ΔL-cspE mRNA by an unidentified endonuclease is not affected. Overall, our data suggest that ribosome-unbound S1 may inhibit translation and stabilize mRNA through the specific inhibition of RNase E-dependent decay.