Increased stability of phage T7g10 mRNA is mediated by either a 5'- or a 3'-terminal stem-loop structure

The mRNA encoding the major capsid protein of phage T7 (T7g10) is highly expressed in Escherichia coli. In common with other highly expressed T7 genes, the 5' end of this mRNA contains a stem-loop structure, while transcription termination at the phage T7 T phi terminator generates a stable 3'-end stem-loop structure. We assessed the influence of these structures on the expression level of T7g10 and on the functional stability of the mRNA. Each one of the 5'- or 3'-hairpin structures was sufficient to increase the functional stability of the T7g10 mRNA more than twofold. A duplication of the 3' T phi-terminator slightly increased 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 suggest 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.