MESSENGER-RNA DEGRADATION IN ESCHERICHIA-COLI - A NOVEL FACTOR WHICH IMPEDES THE EXORIBONUCLEOLYTIC ACTIVITY OF PNPASE AT STEM-LOOP STRUCTURES

Stem-loop structures can protect upstream mRNA from degradation by impeding the processive activities of 3'-5' exoribonucleases. The ability of such structures to impede exonuclease activity in vitro is insufficient to account for the stability they can confer on mRNA in vivo. In this study we identify a factor from Escherichia coli which specifically impedes the processive activity of the 3'-5' exonuclease PNPase at stem-loop structures in vitro. This factor can, potentially, reconcile the apparent. discrepancy between the ability of 3' stem-loop structures to stabilize upstream mRNA in vitro and in vivo. Its mechanism of action, and possible role in regulating mRNA degradation, is discussed.