INCREASED STABILITY OF PHAGE T7G10 MESSENGER-RNA IS MEDIATED BY EITHER A 5'-TERMINAL OR A 3'-TERMINAL STEM-LOOP STRUCTURE

The mRNA encoding the major capsid protein of phage T7 (T7g10) is high ly expressed in Escherichia coli. In common with other highly expresse d T7 genes, the 5' end of this mRNA contains a stem-loop structure, wh ile transcription termination at the phage T7 T Phi terminator generat es a stable 3'-end stem-loop structure. We assessed the influence of t hese structures on the expression level of T7g10 and on the functional stability of the mRNA. Each one of the 5'- or 3'-hairpin structures w as sufficient to increase the functional stability of the T7g10 mRNA m ore than twofold. A duplication of the 3' T Phi-terminator slightly in creased the mRNA stability further. Also, differences in the observed functional half-life could be correlated with the expression level of the T7g10 derivatives when these were partially induced. Our data sugg est that mRNA stabilization by a 5' stem-loop structure can occur even in the absence of a stem-loop structure that protects RNA against 3' exonucleases.