MESSENGER-RNAS CAN BE STABILIZED BY DEAD-BOX PROTEINS

EUBACTERIAL messenger RNAs are synthesized and translated simultaneous ly; moreover the speed of ribosomes usually matches that of RNA polyme rase(1,2). We report here that when in Escherichia coli the host RNA p olymerase is replaced by the eightfold faster bacteriophage T7 enzyme for the transcription of the lacZ gene, the beta-galactosidase yield p er transcript is depressed 100-fold. But the overexpression of DEAD-bo x proteins(3) greatly improves this low yield by stabilizing the corre sponding transcripts. More generally, it stabilizes inefficiently tran slated E. coli mRNAs. Ribosome-free mRNA regions, such as those lying behind the fast T7 enzyme or between successive ribosomes on inefficie ntly translated transcripts, are often unstable(4) and we propose that DEAD-box proteins protect them from endonucleases. These results pinp oint the importance of transcription-translation synchronization for m RNA stability, and reveal an undocumented property of DEAD-box RNA hel icases. These proteins have been implicated in a variety of processes involving RNA(5) but not mRNA stability.