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 tha t this control is dependent on a 5' processing by RNase III. In this p aper, the mechanism of regulation is analyzed by studying the properti es of a pnp-lacZ translational gene fusion. It is shown that this mess age is stable, even when processed by RNase III, and that the degradat ion rate is directly linked to the intracellular concentration of poly nucleotide phosphorylase or to the pnp-lacZ messenger translation rate . Mutations able to decrease the level of repression are all located i n the ribosome loading site. Taken together, these results suggest tha t polynucleotide phosphorylase is able to recognize specifically the p rocessed messenger and to prevent its translation, thus allowing degra dation of the message.