The control of mRNA stability in Escherichia coli: manipulation of the degradation pathway of the polycistronic atp mRNA.

The physical and functional stabilities of genes in the atp operon fall into two classes. The first two genes, atpI and atpB, are rapidly inactivated and degraded at the mRNA level. The remaining seven genes are more stable. In order to investigate how these stabilities are determined, DNA sequences encoding mRNA structures that influence degradative events in other systems, including RNAse III sites and REP sequences, were subcloned or synthesized and inserted into non-coding regions of the operon. The effects of insertion of an RNAse III site depended on whether cleavage left an unstable 3' end or a stabilizing stem-loop upstream of the cutting point. Generation of an unstable 3' end destabilized the neighbouring upstream atp gene, thus modifying the course and rate control of degradation. Removal of the atp transcriptional terminator attenuated expression of the last gene of the operon, atpC. This effect was reversed by substitution of an alternative stem-loop for the terminator. REP sequences inserted into intercistronic regions apparently could not influence rate-controlling steps. The reported data shed light on the factors controlling the inactivation and degradation of genes in the polycistronic atp mRNA, and are discussed in relation to the general role of degradation processes in the control of gene expression.