Stabilization of translationally active mRNA by prokaryotic REP sequences.

The REP sequence is a highly conserved inverted repeat that is present in about 25% of all E. coli transcription units. We show that the REP sequence can stabilize upstream RNA, independently of any other sequences, by protection from 3'-5' exonuclease attack. The REP sequence is frequently responsible for the differential stability of different segments of mRNA within an operon. We demonstrate that REP-stabilized mRNA can be translated in vivo and that cloning the REP sequence downstream of a gene can increase protein synthesis. This provides direct evidence that alterations in mRNA stability can play a role in determining bacterial gene expression. The implications of these findings for the mechanisms of mRNA degradation and for the role of RNA stability in the regulation of gene expression are discussed.