Nucleotide sequence and transcriptional startpoint of the glpT gene of Escherichia coli: extensive sequence homology of the glycerol-3-phosphate transport protein with components of the hexose-6-phosphate transport system

The nucleotide sequences of the glpT gene of Escherichia coli and its regulatory region have been elucidated and the primary structure of the glycerol-3-phosphate transport protein deduced. Extensive amino acid sequence homology was found with two other cytoplasmic membrane proteins: the functionally related hexose-6-phosphate transport protein, and the UHPC protein involved in regulating hexose-6-phosphate uptake. Although no significant amino acid sequence homology was found with other transport proteins, such as the arabinose, citrate, glucose, melibiose, lactose or xylose transporters, all of these proteins share a common secondary structure arrangement with the GLP T protein as they apparently contain twelve membrane-spanning alpha-helical segments. The promoter for glpT was located by transcript mapping and shown to overlap a site to which catabolite activator protein binds in vitro. These findings indicate how catabolite repression may be mediated but do not explain its physiological significance in glycerol metabolism.

Nucleotide sequence and comparative analysis of the frd operon encoding the fumarate reductase of Proteus vulgaris. Extensive sequence divergence of the membrane anchors and absence of an frd-linked ampC cephalosporinase gene

The fumarate reductase of Escherichia coli is a bioenergetically important membrane-bound flavoenzyme consisting of four subunits. A and B comprise a membrane-extrinsic catalytic domain whereas C and D are hydrophobic polypeptides which link the catalytic centres to the electron-transport chain. The nucleotide sequence of the frd operon encoding the fumarate reductase of the distantly related bacterium, Proteus vulgaris has been determined and used to predict the primary structures of the respective subunits. Extensive amino acid sequence identity (greater than 80%) was found between the fumarate reductase A and B subunits of P. vulgaris and E. coli. In contrast, the primary structures of the P. vulgaris and E. coli C and D proteins are much less closely related (about 60% homology) although the overall hydrophobicity of their three membrane-spanning segments has been conserved. In most enteric bacteria, the frd operon is followed by genes, ampR and/or ampC, required for the genetic regulation and biosynthesis of a cephalosporinase. The corresponding region of the P. vulgaris genome is occupied by an operon (orf A'BCD) containing at least four genes which are clearly unrelated to the ampC system. Intriguingly the primary structures of the OrfA and OrfD proteins suggest that, like fumarate reductase, they may be components of a membrane-bound enzyme complex involved in energy metabolism.

An unmodified form of the ColE2 lysis protein, an envelope lipoprotein, retains reduced ability to promote colicin E2 release and lysis of producing cells

Site-directed mutagenesis was used to replace the codon for the N-terminal cysteine residue of pColE2-P9-encoded mature lysis protein (CelB) by an arginine codon. In contrast to the wild-type CelB protein, the product of the mutated gene, which has an altered signal peptidase cleavage site, was neither processed nor acylated. However, the mutant protein retained sufficient residual activity to cause partial, Mg2+-suppressible lysis and could activate envelope phospholipase A1-A2 and promote colicin release, albeit with reduced efficiency compared to the wild-type protein. We propose that the uncleaved signal peptide of the mutant protein acts as the functional equivalent of the fatty acyl groups normally linked to the N-terminal cysteine residue of the wild-type protein, thereby anchoring the protein in the cell envelope where it exerts its various effects.

A single point mutation responsible for c-mos polymorphism in cancer patients

A rare EcoRI restriction fragment length polymorphism (RFLP) in the 3' end of the human c-mos locus has been identified in DNA from patients with breast tumors, esophageal carcinomas and leukemias. Until now, this RFLP has not been found in normal populations, suggesting that its presence may reflect some cancer susceptibility. To characterize this RFLP, we have isolated both alleles of the c-mos locus from DNA of a breast cancer patient and determined the nucleotide sequence of the polymorphic region. Our results show that this RFLP is due to a single nucleotide substitution (T instead of C), resulting in the disappearance of EcoRI site.

Nucleotide sequence and comparative analysis of the human papillomavirus type 18 genome. Phylogeny of papillomaviruses and repeated structure of the E6 and E7 gene products

The complete nucleotide sequence and genomic organization of human papillomavirus type 18, associated with cervical cancer, has been established. A detailed comparative analysis was undertaken leading to the identification of a number of features specific for genital papillomaviruses and the construction of a phylogenetic tree. Genital papillomaviruses differ from other human and animal papillomaviruses as they possess a longer E1 open reading frame (ORF) and have a characteristic control region. Phylogenetically, HPV 18 is located between the benign genital viruses, HPV 6 and HPV 11, and the malignant isolates, HPV 16 and HPV 33, and may represent an evolutionary intermediate among oncogenic papillomaviruses. Viral gene products known to be involved in cellular transformation are those of ORFs E5, E6 and E7. Significant sequence variation was found between the E6 to E7 regions of different integrated forms of HPV 18. On re-examination of the E6 primary structures we noticed that the gene has evolved by successive duplications of a unit encoding 33 amino acids, which include a Cys-X-X-Cys motif. Furthermore, the E7 gene product has apparently evolved in the same manner and is related to E6. Both gene products bear a striking resemblance to the transcriptional factor IIIA of Xenopus laevis, the prototype of a new class of nucleic acid binding proteins.

Molecular genetic analysis of cephalosporinase production and its role in beta-lactam resistance in clinical isolates of Enterobacter cloacae

Two strains of Enterobacter cloacae were isolated from a patient before (strain MHN1) and during (strain MHN2) treatment with moxalactam and gentamicin. Strain MHN1 exhibited inducible ampC cephalosporinase production. In contrast, strain MHN2 expressed the enzyme constitutively at a 3,000-fold higher level. With the Escherichia coli ampC gene as a hybridization probe it was shown that the genomic arrangement of the ampC region was the same in both strains. To gain more insight into regulatory phenomena, the ampC genes were cloned, and their expression was studied in E. coli K-12. The ampC gene from MHN1 behaved normally and conferred inducible beta-lactam resistance. A regulatory region of at least 800 base pairs involved in controlling repression-induction was located immediately upstream of ampC. Surprisingly, when present in E. coli the ampC gene from MHN2 no longer overproduced the cephalosporinase, and inducible expression was observed. This indicates that in MHN2 stable cephalosporinase overproduction is controlled by another factor which is not linked to the ampC gene.

Evolution of the enterobacterial sulA gene: a component of the SOS system encoding an inhibitor of cell division

The LexA-regulated sulA (sfiA) gene of Escherichia coli encodes an unstable protein which inhibits cell division. By determining the nucleotide sequences of the corresponding genes from the related bacteria Salmonella typhimurium, Enterobacter aerogenes and Serratia marcescens it was found that the regulatory region and the LexA binding site (SOS box) have been better conserved during evolution than the coding sequence. The N terminus of the SulA protein [amino acid (aa) residues 1-30] has diverged extensively during the evolution of Enterobacteriaceae, whereas the central region (aa residues 31-149) has been well conserved. At the C terminus a sequence showing some homology to the N protein of phage lambda was detected that may represent a recognition site for the Lon protease, which is known to degrade both polypeptides. When expressed in E. coli, the foreign sulA genes did not block cell division suggesting that their products are inactive. This may indicate that the N terminus of the SulA protein is involved in recognizing the cell division apparatus.

Inducible cephalosporinase production in clinical isolates of Enterobacter cloacae is controlled by a regulatory gene that has been deleted from Escherichia coli

Cephalosporin hyper-resistant Enterobacter cloacae strains are isolated with increasing frequency from hospital infections. Resistance is principally due to the chromosomal ampC gene encoding a cephalosporinase. In contrast to Escherichia coli which expresses ampC constitutively from a promoter located in the upstream frdD gene, E. cloacae displays inducible ampC expression. By cloning the ampC gene it was shown that a linked genetic locus, ampR, mediated the induction by beta-lactams. In the absence of the antibiotic the 30,500 dalton AmpR protein represses ampC expression. The ampR gene shows a highly compact arrangement and is situated between the divergently expressed ampC gene and the frd operon from which it is separated by a bifunctional transcription terminator. The promoters for ampR and ampC substantially overlap and mRNA analyses showed that on induction transcription from the ampC promoter increased greatly whereas that from ampR did not. Two regions of sequence homology flank the ampR gene and it is proposed that a homologous recombination event between these in an ancestral enteric bacterium may have led to the deletion of ampR from the E. coli genome.

Characterization of a bacteriocinogenic plasmid from Clostridium perfringens and molecular genetic analysis of the bacteriocin-encoding gene

The bacteriocinogenic plasmid pIP404 from Clostridium perfringens was isolated and cloned in Escherichia coli, and its physical map was deduced. Expression of the bcn gene, encoding bacteriocin BCN5, is inducible by UV irradiation of C. perfringens and thus resembles the SOS-regulated bacteriocin genes of enteric bacteria. The location of bcn on pIP404 was established by a dot-blot procedure, using specific hybridization probes to analyze mRNA samples from induced and uninduced cultures. From the nucleotide sequence of its gene, the molecular weight of BCN5 was deduced to be 96,591, and a protein of this size was secreted by bacteriocin-producing cultures of C. perfringens. The primary structure of the protein suggests that it may function as an ionophore, since a hydrophobic domain, resembling those of the ionophoric colicins, is present at the COOH terminus. No bacteriocin activity could be detected in E. coli harboring plasmids bearing the bcn gene, even when the transcriptional and translational signals were replaced by those of lacZ. A possible explanation may be found in the unusual codon usage of the adenine-thymine-rich bcn gene, as this shows a preference for codons with a high adenine-plus-thymine content, especially in the wobble position. Many of the frequently used codons correspond to those recognized by minor tRNA species in E. coli. Consequently, bcn expression might be limited by tRNA availability in this bacterium.

Beta-lactam resistance mechanisms in gram-negative bacteria

Beta-lactam antibiotics are commonly used to treat a variety of bacterial infections. Gram-negative bacteria have evolved several resistance mechanisms including altered permeability and beta-lactamase production. New trends in resistance are emerging amongst clinical isolates which may reflect the choice of beta-lactam employed.

beta-Galactosidase and alkaline phosphatase do not become extracellular when fused to the amino-terminal part of colicin N

A series of plasmids encoding hybrid proteins comprising various lengths of the NH2-terminal region of colicin N coupled to almost complete beta-galactosidase or alkaline phosphatase polypeptides was constructed by transposon mutagenesis of ColN plasmid derivatives. Synthesis of the hybrid proteins, like that of colicin N itself, was regulated by the SOS response. Large quantities of the hybrid proteins accumulated in the cytoplasm (beta-galactosidase) or particulate fractions (alkaline phosphatase). When the gene fusions were expressed in cells that were producing colicin E2 and expressing the ColE2 lysis gene, only very low levels of the hybrid proteins were found in the medium. The results suggest that the amino-terminal part of colicin N does not contain sufficient biochemical information to promote the release of the hybrid proteins into the medium.

Genome organization and nucleotide sequence of human papillomavirus type 33, which is associated with cervical cancer

The 7,909-nucleotide sequence of human papillomavirus type 33, which is associated with cervical cancer, has been determined and used to deduce the corresponding genome arrangement. Extensive sequence homologies and other genetic features are shared with the related oncogenic virus, human papillomavirus type 16, especially in the major reading frames. A surprising difference was found in the noncoding region of human papillomavirus type 33 as, unlike all other sequenced papillomaviruses, it contains a perfect 78-base pair tandem repeat.

A mutant of Escherichia coli fumarate reductase decoupled from electron transport

The terminal electron-transfer enzyme fumarate reductase of Escherichia coli is a complex iron-sulfur flavoenzyme composed of four nonidentical subunits organized into two domains: FrdA and -B (a membrane-extrinsic catalytic domain) and FrdC and -D (a transmembrane anchor domain). We have identified a mutation within the membrane-intrinsic domain that alters the electron transfer properties of the iron-sulfur and flavin redox centers of the catalytic domain. Functional electron flow from the quinone analog 2,3-dimethyl-1,4-naphthoquinone or from the electron transport chain is impaired. However, the mutant enzyme can be reduced normally by single-electron donors such as the dye benzyl viologen. The mutant phenotype results from a single A----G transition changing His-82, within the second transmembrane alpha-helix of the FrdC anchor sequence, to an arginine. The mutation, physically located within the anchor domain, is manifested by altered catalytic properties, indicating that the intrinsic and extrinsic domains are conformationally connected. These results confirm the important role of the anchor subunits in functional electron transport and have implications for communication between intrinsic and extrinsic domains of membrane proteins.

The nucleotide sequence of the malT gene encoding the positive regulator of the Escherichia coli maltose regulon

The molecular organization of the malT region of the Escherichia coli K-12 chromosome has been elucidated by nucleotide sequence studies. A single open reading frame of 901 codons comprises the malT gene which is separated by a repetitive extragenic palindromic unit from an unidentified gene, orfX, divergently oriented with respect to malT. The predicted Mr of the MalT protein is 102988, making it the largest transcriptional regulatory protein yet described in E. coli. By deleting in vitro the 3'-end of the gene or constructing malT-lacZ gene fusions, it was found that the integrity of the C-terminus of MalT is indispensable for the activity of the protein. Furthermore, it was found that truncated MalT proteins lacking up to 300 amino acids at the C-terminus blocked the activity of the wild type protein. No sequence homology can be found either with the other activators known in E. coli or with the other proteins of the maltose regulon.

Molecular characterisation of the colicin E2 operon and identification of its products

The DNA sequence of the entire colicin E2 operon was determined. The operon comprises the colicin activity gene, ceaB, the colicin immunity gene, ceiB, and the lysis gene, celB, which is essential for colicin release from producing cells. A potential LexA binding site is located immediately upstream from ceaB, and a rho-independent terminator structure is located immediately downstream from celB. A comparison of the predicted amino acid sequences of colicin E2 and cloacin DF13 revealed extensive stretches of homology. These colicins have different modes of action and recognise different cell surface receptors; the two major regions of heterology at the carboxy terminus, and in the carboxy-terminal end of the central region probably correspond to the catalytic and receptor-recognition domains, respectively. Sequence homologies between colicins E2, A and E1 were less striking, and the colicin E2 immunity protein was not found to share extensive homology with the colicin E3 or cloacin DF13 immunity proteins. The lysis proteins of the ColE2, ColE1 and CloDF13 plasmids are almost identical except in the aminoterminal regions, which themselves have overall similarity with lipoprotein signal peptides. Processing of the ColE2 prolysis protein to the mature form was prevented by globomycin, a specific inhibitor of the lipoprotein signal peptidase. The mature ColE2 lysis protein was located in the cell envelope. The results are discussed in terms of the functional organisation of the colicin operons and the colicin proteins, and the way in which colicins are released from producing cells.

DNA sequence analysis of the Serratia marcescens ompA gene: implications for the organisation of an enterobacterial outer membrane protein

The cloned ompA gene from Serratia marcescens was fully expressed in Escherichia coli and its product correctly assembled into the outer membrane. The S. marcescens polypeptide was not functionally equivalent to the E. coli OmpA protein, which serves as a phage receptor and as a component of several colicin uptake systems. DNA sequence analysis of the gene showed that three regions of the protein likely to be exposed on the cell surface not only differed extensively from the corresponding regions of the E. coli polypeptide but also from all other sequenced OmpA proteins. It is suggested that this sequence polymorphism represents a safety mechanism by which the various enterobacterial species can avoid cross-infection by noxious agents such as phages or colicins.

Molecular characterization of the gene coding for major outer membrane protein OmpA from Enterobacter aerogenes

The ompA gene from Enterobacter aerogenes was subcloned into a low-copy-number plasmid vector and the resultant plasmid, pTU7En, used to study its expression in Escherichia coli K12. Although the gene was strongly expressed and large amounts of OmpA protein were present in the outer membrane its product was not functionally identical to the E. coli polypeptide. In particular, the E. aerogenes OmpA protein was unable to confer sensitivity to OmpA-specific phages of E. coli. When the primary structure of the protein was deduced from the nucleotide sequence of its gene it was found that three domains differed extensively from the corresponding regions of the E. coli protein. As two of these are known to be exposed on the cell surface we inferred that these alterations are responsible for differences in the biological activity of the two proteins.

Gene fusions using the ompA gene coding for a major outer-membrane protein of Escherichia coli K12

It has been shown previously that fragments of the Escherichia coli major outer membrane protein OmpA lacking CO2H-terminal parts can be incorporated into this membrane in vivo [Bremer et al. (1982) Eur. J. Biochem. 122, 223-231]. The possibility that these fragments can be used, via gene fusions, as vehicles to transport other proteins to the outer membrane has been investigated. To test whether fragments of a certain size were optimal for this purpose a set of plasmids was prepared encoding 160, 193, 228, 274, and 280 NH2-terminal amino acids of the 325-residue OmpA protein. The 160-residue fragment was not assembled into the outer membrane whereas the others were all incorporated with equal efficiencies. Thus, if any kind of OmpA-associated stop transfer is required during export the corresponding signal might be present between residues 160 and 193 but not CO2H-terminal to 193. The ompA gene was fused to the gene (tet) specifying tetracycline resistance and the gene for the major antigen (vp1) of foot-and-mouth disease virus. In the former case a 584-residue chimeric protein is encoded consisting NH2-terminally of 228 OmpA residues followed by 356 CO2H-terminal residues of the 396-residue 'tetracycline resistance protein'. In the other case the same part of OmpA is followed by 250 CO2H-terminal residues of the 213-residue Vp1 plus 107 residues partly derived from another viral protein and from the vector. Full expression of both hybrids proved to be lethal. Lipophilic sequences bordered by basic residues, present in the non-OmpA parts of both hybrids were considered as candidates for the lethal effect. A plasmid was constructed which codes for 280 OmpA residues followed by a 31-residue tail containing the sequence: -Phe-Val-Ile-Met-Val-Ile-Ala-Val-Ser-Cys-Lys-. Expression of this hybrid gene was lethal but by changing the reading frame for the tail to encode another, 30-residue sequence the deleterious effect was abolished. It is possible that the sequence incriminated acts as a stop signal for transfer through the plasma membrane thereby jamming export sites for other proteins and causing lethality. If so, OmpA appears to cross the plasma membrane completely during export.

Cloning and molecular characterization of the ompA gene from Salmonella typhimurium

The ompA gene from Salmonella typhimurium, encoding a major heat-modifiable protein of the outer membrane, has been cloned and extensively characterized. When expressed in Escherichia coli the gene directs the synthesis of an OmpA protein which is functionally and topologically indistinguishable from that made in S. typhimurium, thus indicating that export and membrane incorporation are very similar in the two organisms. The S. typhimurium protein effectively substitutes for the E. coli polypeptide in F-dependent conjugation and in the uptake of certain colicins, although it cannot serve as the receptor for the OmpA-specific phages K3 and TuII. On examination of the primary sequence of the protein, predicted from the nucleotide sequence of its gene, it was found that those domains likely to be exposed on the cell surface were significantly different to the corresponding regions of the E. coli polypeptide. These differences in the structure of the two proteins have been used to interpret differences in their biological activities.

Characterisation of the promoter for the LexA regulated sulA gene of Escherichia coli

The sulA gene of Escherichia coli, which encodes an inducible inhibitor of cell division, plays a role in the SOS response. Its expression, like that of other SOS genes, is repressed by the LexA protein. This paper reports the identification and characterisation of the promoter for the cloned sulA gene. The promoter bears good resemblance to the consensus promoter sequence and directs the synthesis of two major RNA species both in vitro and in vivo. Comparison of the sequence around the sulA promoter with the operator sequences of other SOS genes revealed the presence of an SOS box, the LexA protein binding site. This overlaps the -10 region of the promoter and covers the transcriptional initiation sites. LexA protein bound to this SOS box, would, therefore, effectively block transcription.

Apparent bacteriophage-binding region of an Escherichia coli K-12 outer membrane protein

The 325-residue OmpA protein is one of the major outer membrane proteins of Escherichia coli. It serves as the receptor for several T-even-like phages and is required for the action of certain colicins and for the stabilization of mating aggregates in conjugation. We have isolated two mutant alleles of the cloned ompA gene which produce a protein that no longer functions as a phage receptor. Bacteria possessing the mutant proteins were unable to bind the phages, either reversibly or irreversibly. However, both proteins still functioned in conjugation, and one of them conferred colicin L sensitivity. DNA sequence analysis showed that the phage-resistant, colicin-sensitive phenotype exhibited by one mutant was due to the amino acid substitution Gly leads to Arg at position 70. The second mutant, which contained a tandem duplication, encodes a larger product with 8 additional amino acid residues, 7 of which are a repeat of the sequence between residues 57 and 63. In contrast to the wild-type OmpA protein, this derivative was partially digested by pronase when intact cells were treated with the enzyme. The protease removed 64 NH2-terminal residues, thereby indicating that this part of the protein is exposed to the outside. It is argued that the phage receptor site is most likely situated around residues 60 to 70 of the OmpA protein and that the alterations characterized have directly affected this site.

Characterisation of the promoters for the ompA gene which encodes a major outer membrane protein of Escherichia coli

The regulatory region of the ompA gene from Escherichia coli has been characterized by biochemical and genetic approaches. Two overlapping promoters, P1 and P2, organized in that order with respect to the ompA coding sequence, were identified and it was found that ompA possesses an unusually long leader region. Both P1 and P2 were active in an in vitro transcription system although S1 mapping analysis of the ompA mRNA made in vivo showed that P2 was mainly responsible for transcription of the gene. Confirmation of this was obtained by studying down-promoter mutants of ompA cloned in pSC101. These mutants were classified into two groups, deletions and insertions. The deletions, which were caused by the IS102 insertion element found in pSC101 removed the--35 regions of both P1 and P2. However, since P2 was distally situated with respect to the IS element it was less extensively damaged and it is proposed that the residual P2 sequence is responsible for the low level of expression observed. In addition to an IS102 insertion in the promoter region four IS1 insertion mutants were characterized. These had integrated at different positions in the ompA leader region and were all incompletely polar.

Location and nucleotide sequence of frdB, the gene coding for the iron-sulphur protein subunit of the fumarate reductase of Escherichia coli

The frdB gene, encoding the iron-sulphur protein subunit of fumarate reductase, has been located and its complete nucleotide sequence determined. The identity of the gene was confirmed by protein chemical studies and determination of the NH2-terminal sequence of the FrdB protein. The frdB gene is situated distal to and partially overlapped by frdA which codes for the flavoprotein subunit of the reductase. Its reading frame contains 244 codons and predicts a protein of Mr 27092. In composition, the FrdB protein is strikingly similar to the corresponding subunit of the related flavoenzyme, succinate dehydrogenase. Analysis of the protein's primary structure revealed several features characteristic of iron-sulphur proteins.

The nucleotide sequence coding for major outer membrane protein OmpA of Shigella dysenteriae

The nucleotide sequence of the ompA gene from Shigella dysenteriae has been determined and the amino acid sequence of the pro-OmpA protein predicted. Sequence comparison between the ompA genes of S.dysenteriae and Escherichia coli showed that features such as mRNA secondary structure and codon usage, as well as polypeptide function, have been conserved during evolution. The pro-OmpA protein of S.dysenteriae consists of 351 residues, as opposed to the 346 of the E.coli protein and also shows several amino acid changes. These changes have been used to interpret differences in the biological activity of the two proteins.

Nucleotide sequence coding for the flavoprotein subunit of the fumarate reductase of Escherichia coli

The nucleotide sequence of the frdA gene, which encodes the flavoprotein subunit of the fumarate reductase, of Escherichia coli, has been determined. A polypeptide of Mr = 66,052, containing 602 amino acid residues, is predicted. In composition the FrdA protein strongly resembles the flavoprotein subunits of two succinate dehydrogenases. Moreover, a sequence of nine consecutive residues is common to the flavoprotein subunits from fumarate reductase and the beef heart succinate dehydrogenase. This sequence contains a histidyl residue which probably services as the site for attachment of the FAD cofactor to the reductase.

Export of a protein into the outer membrane of Escherichia coli K12. Stable incorporation of the OmpA protein requires less than 193 amino-terminal amino-acid residues

The cloned ompA gene encoding the major outer membrane protein OmpA of Escherichia coli has been shortened in vitro by exonuclease digestion from the end corresponding to the CO2H terminus of the protein. Nine derivatives were identified which still possessed substantial parts of the ompA gene and one was constructed which had suffered a small deletion early in the gene. Gene fragments encoding NH2-terminal OmpA sequences of 45, 133, 193, and 227 residues of the 325 amino acids of OmpA were examined in detail at the DNA level and for OmpA protein fragments synthesized. The latter two fragments were incorporated into the outer membrane and all known functions of the OmpA protein were expressed whereas the fragment with 133 OmpA-specific residues was not stably incorporated into this membrane. In all cases where OmpA functions were observed, an OmpA-specific polypeptide of Mr 24 000 was found in cell envelopes, regardless of the size of the residual ompA sequences and of the fused coding sequences in the vector DNA. Pulse-label experiments revealed larger initial translation products, most of which were degraded to the protein of Mr 24000. The 133-residue OmpA fragment was also detected but proved to be entirely unstable. It is argued that the OmpA protein consists of two domains and that the NH2-terminal moiety from residues 1 to about 180 represents the membrane domain of the polypeptide. Therefore, the loss of about 50, possibly less, CO2H-terminal residues from this domain suffices to interfere with stable incorporation into the outer membrane.

Cloning and expression in Escherichia coli K-12 of the genes for major outer membrane protein OmpA from Shigella dysenteriae, Enterobacter aerogenes, and Serratia marcescens

The outer membranes of many gram-negative bacteria contain a major heat-modifiable protein which shows serological cross-reactivity with the OmpA protein of Escherichia coli K-12. Using the cloned gene for the E. coli K12 protein as a DNA-DNA hybridization probe, we were able to identify the corresponding genes from Shigella dysenteriae. Enterobacter aerogenes, and Serratia marcescens. These were cloned in a phage lambda vector, and their expression in E. coli K-12 was studied. All three OmpA proteins were fully produced and correctly exported to the outer membrane. In several cases, complete or partial restoration of known function of the E. coli K-12 protein was observed.

Genetic and physical characterization of lambda transducing phages (lambda frdA) containing the fumarate reductase gene of Escherichia coli K12

Two types of fumarate reductase transducing phages, lambda frdA, carrying the wild-type frdA gene but differing in the orientation of a R.HindIII fragment of bacterial DNA were isolated from populations of recombinant transducing phages by their ability to complement the lesions of frdA mutants of E. coli. In lysogens, the cloned frdA gene was controlled by its own promoter and was fully responsive to normal regulatory stimuli. The lambda frdA phages would not complement the defects of succinate dehydrogenase (sdh) mutants. Genetic studies showed that the R.HindIII fragment contains ampA, the cis-acting regulatory locus for the chromosomal beta-lactamase gene ampC. No evidence for the presence of other markers was detected but the bacterial segment could be extended to produce plaque-forming phage derivatives containing the amp operon and a gene concerned with bacteriophage morphogenesis, groE(mop). A physical map of the 4.9 kb R.HindIII fragment was constructed by restriction analysis and flanking fragments were identified by DNA:DNA hybridization analysis. The frdA region contained a single asymmetric R.EcoRI target 3.33 kb from one end and the orientation of the physical map with respect to the E.coli linkage map was established.

Production of a soluble form of fumarate reductase by multiple gene duplication in Escherichia coli K12

1. Ampicillin-hyperresistant mutants of Escherichia coli K12 bearing multiple gene duplications in the ampC (beta-lactamase) gene region of the chromosome overproduced at least six proteins with molecular weights 97,000, 80,000, 72,000, 49,000, 33,000 and 26,500 during anaerobic growth. All but two of the proteins (80,000-Mr and 49,000-Mr) were also overproduced during aerobic growth. The distribution of the proteins in soluble and particulate cell fractions was investigated. 2. The 33,000-Mr and 72,000-Mr components were identified as beta-lactamase and the amp-linked frdA gene product, fumarate reductase, respectively. Co-sedimentation of the 26,500-Mr component with the fumarate reductase suggested that the smaller protein could be functionally related to the reductase. The lack of correspondence between the amplified proteins and the products of other amp-linked genes, aspA and mop(groE), indicated that these genes are not included in the repetitive sequence. 3. Fumarate reductase activities were amplified up to 32-fold by the multiple gene duplications. Two forms of fumarate reductase were produced: particulate (membrane-bound) and soluble (cytoplasmic). Production of the soluble form occurred when the binding capacity of the membrane was saturated. Both forms of fumarate reductase were enzymically active but the soluble form was readily inactivated under assay conditions.