No abstract

The amino acid substitutions in the mutant c-subunits of Escherichia coli F1F0-ATPase coded for by the uncE429, uncE408 and uncE463 alleles affect the incorporation of these proteins into the cell membrane. The DNA sequence of the uncE429 allele differed from normal in that a G leads to A base change occurred at nucleotide 68 of the uncE gene, resulting in glycine being replaced by aspartic acid at position 23 in the c-subunit. The uncE408 and uncE463 mutant DNA sequences were identical and differed from normal in that a C leads to T base change occurred at nucleotide 91 of the uncE gene, resulting in leucine being replaced by phenylalanine at position 31 in the c-subunit. An increased gene dosage of the uncE408 or uncE463 alleles resulted in the incorporation into the membranes of the mutant c-subunits. The results are discussed in terms of the 'Helical Hairpin Hypothesis' of Engelman & Steitz [(1981) Cell 23,411-422].

No abstract

The complete nucleotide sequence of the phoS gene, the structural gene for the phosphate-repressible, periplasmic phosphate-binding protein Escherichia coli K-12, was determined. The phosphate-binding protein is synthesized in a precursor form which includes an additional N-terminal segment containing 25 amino acid residues, with the general characteristics of a signal sequence. The amino acid sequence derived from the nucleotide sequence shows the mature protein to be composed of 321 amino acids with a calculated molecillar weight of 34,427. The phoS gene is not part of an operon and is transcribed counterclockwise with respect to the E. coli genetic map. A promoter region has been identified on the basis of homology with the consensus sequence of other E. coli promoter regions. However, an alternative promoter region has been identified on the basis of homology with the promoter regions of the phoA and phoE genes, the structural genes for alkaline phosphatase and outer-membrane pore protein e, respectively.

cysK mutants, deficient in 0-acetylserine sulphydrylase A [O-acetyl-L-serine acetate-lyase (adding hydrogen-sulphide); EC 4.2. gg .8], were isolated as strains resistant to selenite or giving a black colour reaction on bismuth citrate indicator medium. All were resistant to the inhibitor I ,2,4-triazole. Four independent mutants were found which possessed lowered levels of 0-acetylserine sulphydrylase activity and also partially constitutive levels of NADPH-sulphite reductase [hydrogen-sulphide : NADP+ oxidoreductase; EC I .8. I .2]. Strains containing both a cysE mutation and a cysK mutation lacked the constitutive levels of NADPH-sulphite reductase showing that these levels were due to the in vivo concentration of the inducer, 0-acetylserine. The cysK locus was found to be 81 % cotransducible with the ptsI gene.