Polynucleotide phosphorylase of Escherichia coli induces the degradation of its RNase III processed messenger by preventing its translation.

Polynucleotide phosphorylase, a 3' to 5' processive exoribonuclease is post-transcriptionally autocontrolled and it was previously shown that this control is dependent on a 5' processing by RNase III. In this paper, the mechanism of regulation is analyzed by studying the properties of a pnp-lacZ translational gene fusion. It is shown that this message is stable, even when processed by RNase III, and that the degradation rate is directly linked to the intracellular concentration of polynucleotide phosphorylase or to the pnp-lacZ messenger translation rate. Mutations able to decrease the level of repression are all located in the ribosome loading site. Taken together, these results suggest that polynucleotide phosphorylase is able to recognize specifically the processed messenger and to prevent its translation, thus allowing degradation of the message.