FIG. 2.

Plasmids constructed with targeted mutations in the sol operon regulatory region of C. acetobutylicum. Only the regulatory region and the first structural gene (adhE, altered by a six-histidine-encoding tail) are shown; these regions were inserted into the E. coli-C. acetobutylicum shuttle vector pIMP1. P₁ and P₂ are putative promoter structures deduced from primer extension studies. The hairpin symbol indicates a stem-loop structure predicted by the computer program MFold. For further details see the text.