Figure 1.

Plasmids. pSK49 and pSK49Δ-uidA2 express phoB or uidA from P_tac. pSK50 and pSK50Δ-uidA2 express phoB or uidA from P_phoB. A 189-bp P_phoB fragment in pSK58 and pAH85 was generated using PCR. An NdeI site coinciding with the phoB start codon and BamHI site immediately beyond the phoB stop codon were introduced by site-directed mutagenesis. pAH85 has a silent SpeI site at codon 112 of phoB that was introduced with PCR. Mutations were separated by subcloning the respective fragments into pSK58 or pAH85. Only relevant restriction sites are shown. All sites shown for pAH85 are unique. The 2.5-kbp vector backbone is not shown.