DIFFERENTIAL MESSENGER-RNA DECAY WITHIN THE TRANSFER OPERON OF PLASMID R1 - IDENTIFICATION AND ANALYSIS OF AN INTRACISTRONIC MESSENGER-RNA STABILIZER

Processing of the transfer operon mRNA of the conjugative resistance p lasmid R1-19 results in the accumulation of stable traA mRNAs. The sta ble traA transcripts found in vivo have identical 3' ends within downs tream traL sequences, but vary at their 5' ends. The 3' ends determine d coincide with the 3' base of a predicted large clover-leaf-like RNA secondary structure. Here we demonstrate that this putative RNA struct ure, although part of a coding sequence, stabilizes the upstream traA mRNA very efficiently. We also show that the 3' ends of the stable mRN As are formed posttranscriptionally and not by transcription terminati on. Half-life determinations reveal the same half-lives of 13 +/- 2 mi n for the traA mRNAs transcribed from hybrid lac-traAL-cat test plasmi ds, the R1-19 plasmid, and the F plasmid. Protein expression experimen ts demonstrate that the processed stable traA mRNA is translationally active. Partial deletions of sequences corresponding to the predicted secondary structure within the traL coding region drastically reduce t he chemical and functional half-life of the traA mRNA. The results pre sented here unambiguously demonstrate that the proposed secondary stru cture acts as an efficient intracistronic mRNA stabilizer.