Fig. 1. (A) Escherichia coli fdhF mRNA hairpin (Hüttenhofer et al., 1996). Essential nucleotides are indicated by shading. (B) Predicted mRNA hairpin from the M.thermoacetica fdhA gene (GenBank accession No. U73807). Nucleotides identical to the essential nucleotides in E.coli are indicated by shading. (C) Predicted hairpin from the Aquifex aeolicus SelD gene (GenBank accession No. NC_000918). Shading as in (B). Hairpin structures were predicted using the mfold program (Zuker et al., 1999).