Figure 1

Adjustable in vivo papillation assay. (a) Papillation assay plasmid pLHH4. This plasmid contains the MuA transposase-encoding gene under the arabinose-inducible E. coli P_BAD promoter, and the mobilisable mini-Mu reporter transposon Δ_1-8LacZ-Cat-Mu. (b) Generation of papillae. The papillation assay plasmid is transferred into a phenotypically Lac^- E. coli strain. Expression of the transposase protein is induced by arabinose, mobilising the reporter transposon. Transposition of the element into an expressed gene (geneX) in the correct orientation and reading frame will form a geneX::Δ _1-8 lacZ gene fusion, and a β-galactosidase fusion protein will be expressed. Such transposition events can be detected on indicator plates after prolonged incubation as blue microcolonies on otherwise whitish colonies. The level of transposition can be adjusted by varying the transposase expression via changes in arabinose or glucose concentration.