Characterization of the mutant-unc D-gene product in a strain of Escherichia coli K12. An altered beta-subunit of the magnesium ion-stimulated adenosine triphosphatase

Construction and function of chimeric beta subunits containing regions from the beta subunits of the F1F0 ATPases of Escherichia coli and Bacillus megaterium

The highly conserved beta subunit of the Escherichia coli F1F0 ATPase was divided into three sections, each of which was exchanged with the homologous section of the beta subunit of the obligate aerobe Bacillus megaterium. Plasmids coding for the resultant six chimeric beta subunits varied in their abilities to complement two E. coli beta mutants as measured by testing transformed cells for aerobic growth on a nonfermentable carbon source or anaerobic growth on rich medium containing glucose. Two chimeras were able to restore both growth on succinate and anaerobic growth on rich medium. The genetic results corresponded to increased levels of membrane-bound ATPase and ATP synthase activities. These chimeric subunits were therefore capable of being assembled into functional E. coli ATPase complexes. The results indicate that chimeric beta subunits can be used to analyze assembly of the beta subunit and that the final 181 amino acids of the beta subunit might contain a region involved in functional energy coupling.

The role of arginine in the conserved polar loop of the c-subunit of the Escherichia coli H(+)-ATPase

The Arg-41 of the c-subunit of the F0F1-ATPase of Escherichia coli has been changed by site-directed mutagenesis to Glu, Leu or Lys. None of the mutants can carry out oxidative phosphorylation. No detectable F1-ATPase activity is found on the membranes and only small amounts in the cytoplasm. Two-dimensional gel electrophoresis shows that in all three mutant strains the assembly of the F0F1-ATPase has been affected. When plasmids carrying the mutant genes, together with other normal unc genes, were inserted into strains each carrying a mutation in one of the unc genes other than uncE their capacity for oxidative phosphorylation was reduced or eliminated, the effect being most pronounced with the uncG and uncC mutants and least pronounced with the plasmid giving the Arg-->Lys substitution. The c-subunit is a multimer in the ATP synthase complex and it appears that a mixture of normal and mutant gene products allows assembly of a functional complex.

The chloroplast beta-subunit allows assembly of the Escherichia coli F0 portion of the energy transducing adenosine triphosphatase

The effect of the expression of the chloroplast F1-ATPase beta-subunit in two Escherichia coli beta-subunit mutant strains was investigated. The amount of chloroplast beta-subunit formed in E. coli was increased by introducing a 'Shine-Dalgarno' sequence upstream from the translation start site. The chloroplast beta-subunit was membrane bound but was unable to functionally replace the mutant beta-subunit in a strain carrying the uncD409 allele [corrected]. However, in an E. coli mutant strain unable to form the beta- and epsilon-subunits the presence of the chloroplast beta-subunit enabled the assembly of a functional proton pore [corrected]

Mutations within the uncE gene affecting assembly of the F1F0-ATPase of Escherichia coli

Site-directed mutagenesis has been used to construct two mutations within the uncE gene, which codes for the c-subunit of the F1F0-ATPase, resulting in the substitution of glycine-27 by leucine and of glycine-32 by leucine. Strains carrying each mutation are unable to grow on minimal medium containing succinate as the sole carbon source and possess an uncoupled growth yield. Membranes prepared from strains carrying each mutation possess low levels of ATPase activity and are proton-impermeable. The c-subunit in each mutant strain appears to assemble into the F0-ATPase and disrupt the normal assembly of the F1-ATPase. The results are discussed in relation to a previously proposed model for the F0 sector [Cox, Fimmel, Gibson & Hatch (1986) Biochim. Biophys. Acta 849, 62-69].

Random mutagenesis of the gene for the beta-subunit of F1-ATPase from Escherichia coli

ATP synthesis by oxidative phosphorylation in Escherichia coli occurs in catalytic sites on the beta-subunits of F1-ATPase. Random mutagenesis of the beta-subunit combined with phenotypic screening is potentially important for studies of the catalytic mechanism. However, when applied to haploid strains, this approach is hampered by a preponderance of mutants in which assembly of F1-ATPase in vivo is defective, precluding enzyme purification. Here we mutagenized plasmids carrying the uncD (beta-subunit) gene with hydroxylamine or N-methyl-N'-nitro-N-nitrosoguanidine and isolated, by phenotypic screening and complementation tests, six plasmids carrying mutant uncD alleles. When the mutant plasmids were used to transform a suitable uncD- strain, assembly of F1-ATPase in vivo occurred in each case. Moreover, in one case (beta Gly-223----Asp) F1-ATPase assembly proceeded although it had previously been reported that this mutation, when present on the chromosome of a haploid strain, prevented assembly of the enzyme in vivo. Therefore, this work demonstrates an improved approach for random mutagenesis of the F1-beta-subunit. Six new mutant uncD alleles were identified: beta Cys-137----Tyr; beta Gly-142----Asp; beta Gly-146----Ser; beta Gly-207----Asp; beta-Gly-223----Asp; and a double mutant beta Pro-403----Ser,Gly-415----Asp which we could not separate. The first five of these lie within or very close to the predicted catalytic nucleotide-binding domain of the beta-subunit. The double mutant lies outside this domain; we speculate that the region around residues beta 403-415 is part of an alpha-beta intersubunit contact surface. Membrane ATPase and ATP-driven proton pumping activities were impaired by all six mutations. Purified F1-ATPase was obtained from each mutant and shown to have impaired specific ATPase activity.

Synthesis of maize chloroplast ATP-synthase beta-subunit fusion proteins in Escherichia coli and binding to the inner membrane

The maize chloroplast gene for the beta subunit (atpB) of the chloroplast CF1 component of ATPase from maize, when fused to either the lacZ or ral genes in the vectors pMC1403 or pHUB4, is expressed in Escherichia coli as a fusion protein with beta-galactosidase or with bacteriophage lambda Ral sequences. Some of the fusion proteins are converted to a membrane-bound form, as determined by differential and sucrose-gradient centrifugation. The specificity of membrane binding has been examined using E. coli unc mutants that are defective in binding of the F1 ATPase component to the F0 receptor site on the membrane, and by the use of two different length maize atpB::lacZ gene fusions. We show that the first 365 N-terminal amino acids (aa) of the maize beta subunit are involved in binding to the E. coli inner membrane, and that this binding is probably mediated by the bacterial F0 receptor.

Intracistronic mapping of the defective site and the biochemical properties of beta subunit mutants of Escherichia coli H+-ATPase: correlation of structural domains with functions of the beta subunit

Sixteen mutants of Escherichia coli defective in H+-ATPase (proton-translocating ATPase) were tested for their ability to recombine with hybrid plasmids carrying various portions of the beta subunit cistron. Twelve mutations were mapped within the carboxyl half of the cistron corresponding to amino acid residues 279 to 459 (domain II), while four mutations were mapped within residues 17 to 278 (domain I). The biochemical properties of these mutants were analyzed in terms of the proton permeability of their membranes and the assembly properties of their F1F0 complex. The mutants were classified according to the properties into three types, I, II, and III. In 12 mutants of type I, proton conduction in membrane vesicles was blocked and little F1 was released from the membranes under conditions in which F1 could be released from wild-type membranes, suggesting that assembly of the F1F0 complex is structurally and functionally defective. F1 was partially purified with very low recovery from one of the type I mutants, KF16. ATPase activity was reconstituted from this F1 with the beta subunit of the wild type, confirming the genetic results. Only one mutant, KF38, was classified as type II. Its membranes were partially leaky to protons and its F1 was releasable, suggesting that the interaction of its F1 and F0 was unstable. Type III mutants, KF11 and KF43, had an F1F0 complex with very low activity, in which the structure of F1 was relatively similar to that of the wild type. F1 was purified as a single complex from KF43 in this study and from KF11 previously (H. Kanazawa, Y. Horiuchi, M. Takagi, Y. Ishino, and M. Futai (1980) J. Biochem. 88, 695-703). Reconstitution experiments in vitro showed that the F1's of both mutants were defective in the beta subunit. The properties of the altered F1 of KF43 differed from those of F1 of KF11, suggesting that the mutation sites of KF43 and KF11 were different. From the results of mapping mutation sites and the biochemical properties of the mutants, the correlation of structural domains with function of the beta subunit is discussed. Most type I and type II mutations except that of KF39 were mapped in domain II, while the type III mutations were mapped in domain I, suggesting that domain II is more important than domain I for the function of the beta subunit, especially in terms of proper assembly of the F1F0 complex.

Use of lambda unc transducing bacteriophages in genetic and biochemical characterization of H+-ATPase mutants of Escherichia coli

The eight subunits of the H+-ATPase of Escherichia coli are coded by the genes of the unc operon, which maps between bglB and asnA. A collection of unc mutations were transferred via P1 transduction into a strain in which lambda cI857 S7 was inserted into bglB. The lambda phage was induced, and asnA+ transducing phage that carried unc were selected. Transducing phage carrying mutations in the uncA, B, D, E, and F genes were used for complementation analysis with a collection of unc mutants, including mutants which had been reported previously but not genetically characterized. Some mutations gave a simple complementation pattern, indicating a single defective gene, whereas other mutations gave more complex patterns. Two mutants (uncE105 and uncE107) altered in the proteolipid (omega) subunit of F0 were not complemented by any of the lambda unc phage, even though both mutants had a fully functional F1 ATPase and therefore normal A and D genes. Hence, only limited conclusions can be drawn from genetic complementation alone, since it cannot distinguish normal from abnormal genes in certain classes of unc mutants. The lambda unc phage proved to be essential in characterizing several mutants defective in F0-mediated H+ translocation. The unc gene products were overproduced by heat induction of the lysogenized lambda unc phage to determine whether all the F0 subunits were in the membrane. Two mutants that gave a simple complementation pattern, indicative of one defective gene, did not assemble a three-subunit F0. The uncB108 mutant was shown to lack the chi subunit of F0 but to retain psi and omega. Trace amounts of an altered omega subunit and normal amounts of chi and psi were found in the uncE106 mutant. A substitution of aspartate for glycine at residue 58 of the protein was determined by DNA sequence analysis of the uncE gene cloned from the lambda uncE106 phage DNA. One of the omega-defective, noncomplementing mutants (uncE107) was shown to retain all three F0 subunits. The uncE gene from this mutant was also sequenced to confirm an asparagine-for-aspartate substitution at position 61 (the dicyclohexylcarbodiimide-binding site) of the omega subunit.

Oxidative phosphorylation in Escherichia coli. Characterization of mutant strains in which F1-ATPase contains abnormal beta-subunits

To facilitate study of the role of the beta-subunit in the membrane-bound proton-translocating ATPase of Escherichia coli, we identified mutant strains from which an F1-ATPase containing abnormal beta-subunits can be purified. Seventeen strains of E. coli, characterized by genetic complementation tests as carrying mutations in the uncD gene (which codes for the beta-subunit), were studied. The majority of these strains (11) were judged to be not useful, as their membranes lacked ATPase activity, and were either proton-permeable as prepared or remained proton-impermeable after washing with buffer of low ionic strength. A further two strains were of a type not hitherto reported, in that their membranes had ATPase activity, were proton-impermeable as prepared, and were not rendered proton-permeable by washing in buffer of low ionic strength. Presumably in these two strains F1-ATPase is not released in soluble form by this procedure. F1-ATPase of normal molecular size were purified from strains AN1340 (uncD478), AN937 (uncD430), AN938 (uncD431) and AN1543 (uncD484). F1-ATPase from strain AN1340 (uncD478) had 15% of normal specific Mg-dependent ATPase activity and 22% of normal ATP-synthesis activity. The F1-ATPase preparations from strains AN937, AN938 and AN1543 had respectively 1.7%, 1.8% and 0.2% of normal specific Mg-dependent ATPase activity, and each of these preparations had very low ATP-synthesis activity. The yield of F1-ATPase from the four strains described was almost twice that obtained from a normal haploid strain. The kinetics of Ca-dependent ATPase activity were unusual in each of the four F1-ATPase preparations. It is likely that these four mutant uncD F1-ATPase preparations will prove valuable for further experimental study of the F1-ATPase catalytic mechanism.

The Leeuwenhoek Lecture, 1981. The biochemical and genetic approach to the study of bioenergetics with the use of Escherichia coli: progress and prospects

How the 'energy currency' of the cell, adenosine triphosphate (ATP), is produced consequent upon the oxidation of foodstuffs (oxidative phosphorylation) is, despite prolonged research, still a matter of debate and the molecular mechanism of the process is unknown. It appears that the problem of oxidative phosphorylation can be approached with the aid of the biochemical genetics of the bacterium Escherichia coli. The ease of manipulation of bacteria and definitive results obtained by this approach have been invaluable in solving other major biochemical problems. Mutants affected in oxidative phosphorylation have been isolated and characterized by genetic and biochemical techniques. These 'unc' mutants are affected in the adenosine triphosphatase (ATPase) multiprotein complex which is part of the cell membrane and responsible for the terminal stages of ATP synthesis. Seven distinct genes concerned with oxidative phosphorylation have been characterized in E. coli and shown to be part of an operon. The relationships between the different classes of unc genes and the various components of the ATPase have been established. Information about the assembly of the ATP synthesizing complex in the cell membrane has also been obtained and the stage set for further studies on the assembly, control and function of the ATP synthesizing system.

Three genes coding for subunits of the membrane sector (F0) of the Escherichia coli adenosine triphosphatase complex

Two mutant unc alleles, unc-469 and unc-476, have been characterized as affecting a previously undescribed gene, designated uncF. The uncF gene is part of the unc operon (with the gene order being uncBFEAGDC), although some uncertainty remains as to the relative order of the uncF and uncE genes. Mutant strains carrying the uncF469 or uncF476 allele lack the 18,000-molecular-weight component of the F0 sector of the adenosine triphosphatase in the cell membrane but retain the dicyclohexylcarbodiimide-binding protein (molecular weight, 8,400). Conversely, strains carrying mutations in the uncE gene lack the dicyclohexylcarbodiimide-binding protein but retain the 18,000-molecular-weight protein in the cell membrane. Strains carrying mutations in the uncB gene have both the 18,000-molecular-weight protein and the dicyclohexylcarbodiimide-binding protein present in the cell membranes. The three proteins of the F0 portion of the adenosine triphosphatase, viz., 24,000, 18,000, and 8,400 molecular weights, became membrane associated after in vitro transcription-translation with plasmid pAN51 as template. Plasmids carrying deletions which affected the UncBFE region were isolated from plasmid pAN51 and characterized genetically. A comparison of the genes that were absent from the various deletion plasmids with the membrane-associated products formed after in vitro transcription-translation indicated that the uncB gene coded for the 24,000-molecular-weight protein and that the gene order was probably uncBFE. A correlation between length of deoxyribonucleic acid, genes present, and their products is presented in relation to plasmid pAN51.

Organization of unc gene cluster of Escherichia coli coding for proton-translocating ATPase of oxidative phosphorylation

The proton-translocating ATPase (F1-F0) of oxidative phosphorylation (ATP phosphohydrolase, EC 3.6.1.3) is coded for by a set of structural genes comprising the unc operon in Escherichia coli. We have analyzed several new transducing phages and plasmids carrying various lengths of the DNA segments of the unc operon by complementation assay using 14 new unc- mutants and representatives of previously described strains which were made available to us. Transducing phages carrying parts of the unc gene cluster were isolated: lambda uncA-9 and lambda glmS phages converted only some of the unc- mutants to the Unc+, as determined by complementation assays. A new hybrid plasmid (pMCR533) carrying part of the unc operon was constructed by inserting the HindIII fragment of lambda asn-5 DNA (a phage carrying the entire unc operon) into the unique HindIII site of pBR322. This plasmid transformed eight unc- strains to Unc+, including uncB402 and uncA401, but did not complement uncD11 or four other strains. Two minichromosomes which carry the E. coli replication origin were also tested: plasmid pNH05 transformed the uncB402 but not the uncA401 strain to Unc+, whereas plasmid pMCF1 transformed none of the mutants tested. Analysis of the DNAs from these transducing phages and plasmids with restriction endonucleases suggested that all of the structural genes for the F1-F0 complex are localized within a DNA segment of approximately 4.5 megadaltons containing two EcoRI sites. The approximate locations of the unc- mutations were mapped on this DNA segment.

Subunits of the adenosine triphosphatase complex translated in vitro from the Escherichia coli unc operon

The unc operon of Escherichia coli was split into two fragments by the restriction endonuclease HindIII. The operator-proximal portion was cloned into plasmid pACYC184, forming plasmid pAN51, which included the genes uncB, uncE, and uncA. When plasmid pAN51 was used as template in an in vitro transcription/translation system, the alpha subunit (from the uncA gene) and delta subunit of the F(1) adenosine triphosphatase (ATPase) were formed. In addition, three polypeptides of molecular weights 18,000, 17,000, and 14,000 were formed, and the significance of these polypeptides is discussed. The operator-distal portion of the unc operon was also cloned into plasmid pACYC184, forming plasmid pAN36, which included the uncD and uncC genes. When this plasmid was used as template in an in vitro transcription/translation system, the beta subunit (from the uncD gene) and the epsilon subunit (from the uncC gene) of the F(1) ATPase were formed. A polypeptide of a molecular weight similar to the epsilon subunit but of different net charge was also formed. Plasmid pAN45, carrying the complete unc operon, was isolated after digestion of a mixture of plasmids pAN51 and pAN36 with the restriction endonuclease HindIII and then religation with T4 deoxyribonucleic acid ligase. It was concluded that a HindIII restriction site occurred within the newly described uncG gene, which was shown, by complementation studies with Mu-induced mutants, to be located between the uncA and uncD genes to give the gene order uncBEAGDC. The uncG gene appears to code for the gamma subunit of the F(1) ATPase.

The ATP synthetase of Escherichia coli K12: purification of the enzyme and reconstitution of energy-transducing activities

The ATP synthetase of Escherichia coli K12 was purified by a simple procedure. The dicyclohexylcarbodiimide-sensitive ATPase activity was enriched 21-fold. The ATP synthetase preparation contained the eight polypeptides (alpha, beta, gamma, a,delta, b,espilon, c) of the enzyme and a residual contamination (4% of the total protein) as shown by dodecylsulfate/polyacrylamide electrophoresis. The polypeptide c was specifically labelled with [14C]dicyclohexylcarbodiimide. Energy-transducing activities were reconstituted from soybean phospholipids and the purified enzyme. The proteoliposomes exhibited a significantly higher ATP-32Pi exchange activity and a higher proton-translocating activity as compared to the untreated membranes.

The uncA gene codes for the alpha-subunit of the adenosine triphosphatase of Escherichia coli. Electrophoretic analysis of uncA mutant strains

Four mutant strains of Escherichia coli which lack membrane-bound adenosine triphosphatase activity were shown by genetic-complementation tests to carry mutations in the uncA gene. A soluble inactive F1-ATPase aggregate was released from the membranes of three of the uncA mutant strains by low-ionic-strength washing, and purified by procedures developed for the purification of F1-ATPase from normal strains. Analysis of the subunit structure by two-dimensional gel electrophoresis indicated that the F1-ATPase in strains carrying the uncA401 or uncA453 alleles had a subunit structure indistinguishable from normal F1-ATPase. In contrast, the F1-ATPase from the strain carrying the uncA447 allele contained an alpha-subunit of normal molecular weight, but abnormal net charge. Membranes from strains carrying the uncA450 allele did not have F1-ATPase aggregates that could be solubilized by low-ionic-strength washing. However, a partial dipolid strain carrying both the uncA+ and uncA450 alleles formed an active F1-ATPase aggregate which could be solubilized by low-ionic-strength washing of the membranes and which contained two types of alpha-subunit, one of which was normal and the other had abnormal net charge. It is concluded that the uncA gene codes for the alpha-subunit of the adenosine triphosphatase.

Properties of membranes from mutant strains of Escherichia coli in which the beta-subunit of the adenosine triphosphatase is abnormal

Five uncoupled mutant strains of Escherichia coli carrying mutations in the uncD gene have been studied. In each of these mutant strains the beta-subunit of the F1 portion of the membrane-bound adenosine triphosphatase is abnormal. In one of the mutant strains (carrying the uncD12 allele) in F1-ATPase aggregate was formed which was purified and found to have low ATPase activity. ATPase activity was absent in the other four strains and the abnormal beta-subunits were tightly bound to the membranes. However, membranes from these strains exhibited various proton permeabilities as indicated by NADH-dependent atebrin-fluorescence quenching and bound different amounts of normal F1-ATPase. The amounts of reconstitution of energy-linked reactions after the addition of normal F1-ATPase also varied depending on the mutant allele. It is apparent that considerable phenotypic variations can occur between strains carrying mutations in the same unc gene.

Solubilization of adenosine triphosphatase from membranes of Escherichia coli: effect of p-aminobenzamidine

The five subunits of the membrane-bound adenosine triphosphatase (F1) from Escherichia coli were identified on electrophoretograms of membranes which had been washed with a low-ionic-strength buffer containing the protease inhibitor p-aminobenzamidine. All of the subunits of the membrane-bound F1 appeared to have the same molecular weights and isoelectric points as those of the soluble F1, as judged by two-dimensional electrophoresis. p-Aminobenzamidine inhibited the solubilization of F1 rebound to F1-depleted membranes, and was found to inhibit the membrane-bound adenosine triphosphatase activity to a much greater extent than the solubilized activity. It is therefore unlikely that p-aminobenzamidine inhibits the solubilization of F1 by inhibiting a protease, as suggested previously by Cox et al. (G.B. Cox, J.A. Downie, D.R.H. Fayle, F. Gibson, and J. Radik, J. Bacteriol. 133:287--292, 1978).

Specialized transducing phage lambda carrying the genes for coupling factor of oxidative phosphorylation of Escherichia coli: increased synthesis of coupling factor on induction of prophage lambda asn

Studies were made of the synthesis of the coupling factor complex (F1--F0) of oxidative phosphorylation after prophage induction of a set of Escherichia coli strains lysogenic for defective transducing phage lambda asn, lambda uncA, or lambda bglC. The transducing phages had been isolated from a strain of E. coli carrying prophage lambda cI857 S7 within the bglB gene located near the unc gene cluster [Miki, T., Hiraga, S., Nagata, T. & Yura, T. (1978) Proc. Natl. Acad. Sci. USA 75, 5099--5103]. When lysogenic cells carrying lambda asn and lambda cI857 S7 were induced at high temperature, synthesis of the F1-ATPase portion of the complex increased to severalfold that of the noninduced cells. In contrast, no increase was observed upon thermoinduction of cells carrying lambda uncA or lambda bglC. The number of membrane sites that could bind purified F1-ATPase also increased significantly upon induction by lambda asn but not by lambda uncA or lambda bglC. In addition, F1-depleted membranes prepared from lambda asn-induced bacteria required more dicyclohexylcarbodiimide to seal the proton pathway than did those from noninduced bacteria. These results strongly suggest that lambda asn carries a set of bacterial genes coding for all the F1 polypeptides (the alpha, beta, gamma, delta, and probably the epsilon subunits) and at least some of the genes involved in formation of F0 polypeptides. Although lambda uncA carries the structural gene (uncA) for the alpha subunit of F1-ATPase, it apparently does not carry the whole set of F1--F0 genes.

A fifth gene (uncE) in the operon concerned with oxidative phosphorylation in Escherichia coli

Three mutant unc alleles (unc-408, unc-410, and unc-429) affecting the coupling of electron transport to oxidative phosphorylation in Escherichia coli K-12 have been characterized. Genetic complementation analyses using previously defined mutant unc alleles indicated that the new mutant unc alleles affect a previously undescribed gene designated uncE. The phenotype of strains carrying the uncE408 or uncE429 allele is similar in that Mg(2+)-adenosine triphosphatase activity is only found in the cytoplasmic fraction, and membranes do not bind the F(1) portion of adenosine triphosphatase purified from a normal strain. In contrast, adenosine triphosphatase activity is present both in the cytoplasm and on the membranes from a strain carrying the unc-410 allele, and normal F(1) binds to F(1)-depleted membranes from this strain. The adenosine triphosphatase solubilized from membranes of a strain carrying the unc-410 allele reconstituted ATP-dependent membrane energization in F(1)-depleted membranes from a normal strain. Genetic complementation tests using various Mu-induced unc alleles in partial diploid strains show that the uncE gene is in the unc operon and that the order of genes is uncB E A D C. The unc-410 allele differs from the uncE408 and uncE429 alleles in that complementation tests with the Mu-induced unc alleles indicate that more than one gene is affected. It is concluded that this is due to a deletion which includes part of the uncE gene and another gene, or genes, between the uncE and uncA genes.

The yeast mitochondrial ATPase complex. Subunit composition and evidence for a latent protease contaminant

1. The subunit compositions of the F1 (oligomycin-insensitive) and F1--F0 (oligomycin-sensitive) mitochondrial ATPase complexes from Saccharomyces cerevisiae have been examined by the highly resolving technique of sodium dodecyl sulphate-polyacrylamide slab gel electrophoresis using a discontinuous buffer system. When isolated in the presence of protease inhibitors, F1 and F1--F0 contained five and twelve bands, respectively; this contrasts with the four- and ten-band patterns seen previously using the less resolving disc gel method. When isolated in the absence of protease inhibitors both F1 and F1--F0 contain spurious polypeptides produced by proteolytic modification. 2. Endogenous protein turnover in S. cerevisiae was impaired in the presence of protease inhibitors. F1--F0 isolated from cells grown in the presence and absence of inhibitors contained an identical polypeptide composition, suggesting that the subunits are not significantly modified by endogenous proteases prior to cell harvesting. 3. Yeast F1--F0 prepared in the presence of protease inhibitors contains a latent, sodium dodecyl sulphate-activated protease contaminant. Sodium dodecyl sulphate-induced proteolysis is largely confined to the 52 000 dalton alpha subunit which degrades into polypeptides of 40 000 and 10 700 daltons. The 40 000 dalton band is apparently equivalent to the polypeptide previously designated subunit 3. 4. Both F1 and F1--F0 were isolated from Torulopsis glabrata, a yeast with considerably shorter mitochondrial DNA than that in S. cerevisiae. F1--F0 catalysed high rates of ATP--32Pi exchange when reconstituted into phospholipid vesicles, thus demonstrating the presence of a complete coupling mechanism. F1--F0 contained approximately twelve subunits and F1 five, like the S. cerevisiae complexes. It therefore appears that the shorter mitochondrial DNA length does not produce a significantly simpler ATPase subunit structure.