A stable core region of the tra operon mRNA of plasmid R1-19

The degradation of the polycistronic tra-mRNA of the resistance plasmid R1-19 leads to the accumulation of a well defined series of stable mRNA species. The majority of the most stable mRNAs contains the message for the traA gene only. The differently sized stable mRNAs possess a common 3'terminus within the traL gene but vary at their 5' ends. The 3'terminus probably results from protection against exoribonucleases by a secondary structural feature. We propose that the 5' ends are generated by endoribonucleolytic cleavage. The stability of this part of the tra-mRNA exceeds 30 minutes and probably increases the rate of expression of the traA gene product propilin, the precursor of the sex pilus subunit. The expression of propilin and its processing into a protein of the molecular weight of mature pilin is demonstrated with the isolated gene. The sequence of the so far unknown genes traL and traE of R1-19 is presented.