mRNAs can be stabilized by DEAD-box proteins

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Abstract
EUBACTERIAL messenger RNAs are synthesized and translated simultaneously; moreover the speed of ribosomes usually matches that of RNA polymerase1,2. We report here that when in Escherichia coli the host RNA polymerase is replaced by the eightfold faster bacteriophage T7 enzyme for the transcription of the lacZ gene, the β-galactosidase yield per transcript is depressed 100-fold. But the overexpression of DEAD-box proteins3 greatly improves this low yield by stabilizing the corresponding transcripts. More generally, it stabilizes inefficiently translated E. coli mRNAs. Ribosome-free mRNA regions, such as those lying behind the fast T7 enzyme or between successive ribosomes on inefficiently translated transcripts, are often unstable4 and we propose that DEAD-box proteins protect them from endonucleases. These results pinpoint the importance of transcription–translation syn-chronization for mRNA stability, and reveal an undocumented property of DEAD-box RNA helicases. These proteins have been implicated in a variety of processes involving RNA5 but not mRNA stability.