, Volume 248, Issue 5, pp 599-609

Translational coupling and limited degradation of a polycistronic messenger modulate differential gene expression in theparD stability system of plasmid R1

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TheparD stability system of plasmid R1 is an auto-regulated operon containing two genes,kis andkid, that code, respectively, for a killer protein (Kid) and for an antagonist of Kid action (Kis protein). A polycistronic transcript and a shorter mRNA, coding only for Kis and ending in a stem-loop sequence, have been identified as the mainparD transcripts in cells carrying a derepressedparD operon. In this communication we show that bothparD mRNAs have a half-life close to 1 min and are present in similar amounts. Using an assay based on cell-free extracts ofEscherichia coli, we demonstrate that the shortkis mRNA originates from limited degradation of the bicistronicparD transcript and that the stem-loop structure within the 5′ end of thekid gene is specifically required for the formation of this short transcript. In vivo experiments show that synthesis of Kis is required for efficient synthesis of Kid. These data indicate that RNA processing and translational coupling are important mechanisms that modulate the differential expression of the two genes,kis andkid, in the bicistronicparD operon.

Communicated by R. Devoret