K⁺-sparing phenotype in liquid cultures. Growth rates of isogenic pairs of strains are plotted as a function of [K⁺]_e. The pairs were TL1105A (●) and its kdp-208 derivative GJ1400 (○) and transformants of TL1105A with either plasmid vector pTrc99A (■) or its derivative, pHYD724, carrying the cloned parental kdpA′ ORF (□). All cultures were grown in media of pH 7 at 34°C; for the latter pair of strains, the media were additionally supplemented with ampicillin and 0.03 mM IPTG.

Molecular characterization of kdp-208 mutation. (A) Proximal part (to scale) of the kdp operon, including its start site of transcription (+1), extent of the kdpF and kdpA ORFs (open bars), and location in TL1105A of kdpA::Mu d1lac(λ) insertion (shown as inverted triangle; length not to scale). The hatched bar denotes the extent of a 432-bp PCR product used in several experiments described in the text. Also marked are the EcoRI (E) and HindIII (H) sites in the kdp promoter and Mu S end, respectively, that are discussed in the text. (B) Nucleotide sequence (top strand) of the kdp::Mu-lac fusion region in parental strain TL1105A from the start of the kdpA ORF to the HindIII site in Mu S; the nucleotide numbering is indicated to the left of each line. The Mu S region sequence is taken from published data (21, 32), and the junction between the kdpA (17) and Mu S sequences is indicated by a vertical arrow. The perfect inverted repeat within Mu S is shown overlined by the pair of convergent arrows. The 22-bp deletion (-Δ-) and the sequence of the 8-nucleotide substitution that together make up the kdp-208 mutation are depicted beneath the wild-type sequence. Pentameric direct repeats in the vicinity of the deletion are boxed. Beneath the nucleotide sequence is the sequence of the conceptual translation product (in the one-letter amino acid code) for the kdp-208 mutant; also included in the region of the deletion is the short altered C-terminal sequence (ending with ∗) inferred for the polypeptide encoded by the parental strain.

K⁺-sparing phenotype and kdp-lac repression in trans. Plotted are the β-galactosidase specific activities (in Miller units [22]) as a function of [K⁺]_e for isogenic strains carrying the kdp-lac plasmid pHYD700: GJ1413 (parental [□]) and GJ1414 (kdp-208 [■]).

K⁺-sparing plate phenotype associated with kdp-208. The following isogenic pairs of strains (designated parental and kdp-208 within each pair) were streaked on medium containing 7 mM [K⁺]_e and incubated for 40 h. Sectors 1 and 2, lysogens of GJ1417 with phages λpTL1105 (parental) and λpGJ1400 (kdp-208), respectively; sectors 3 and 4, transformants of TK2205 with pHYD712 (parental) and pHYD711 (kdp-208), respectively; and sectors 5 and 6, pHYD700 transformants of GJ1414 (kdp-208) and GJ1413 (parental), respectively.

K⁺-sparing phenotype associated with IPTG-induced overexpression of parental KdpA′. Growth curves for strain TL1105A/pHYD724 in 7 mM [K⁺]_e medium supplemented with 0 (■), 10 (▴), or 40 (▵) μM IPTG are shown.