Cleavage within an RNase III site can control mRNA stability and protein synthesis in vivo.

We report that processing at a cloned bacteriophage T7 RNase III site results in strong stabilization of the mRNA relative to the full-length transcript. In contrast, processing by RNase III of the bacteriophage lambda int transcript leads to rapid degradation of the messenger. It is proposed that the mode of cleavage within the RNase III site determines mRNA stability. Single cleavage leaves part of the phage T7 RNase III site in a folded structure at the generated 3' end and stabilizes the upstream mRNA whereas double cleavage at the lambda int site removes the folded structure and accelerates degradation. In addition, the processed transcript is as active a messenger as the unprocessed one and can direct protein synthesis for longer times. This increased efficiency is accompanied by a proportional (3-4 fold) increase in protein levels. In contrast, processing at the lambda int site reduces Int synthesis. Thus, processing may either stabilize mRNA and stimulate gene expression or destabilize a messenger and prevent protein synthesis. The end result appears to be determined by the mode of cleavage within the RNase III site.