Conditional expression of the vesicular stomatitis virus glycoprotein gene in Escherichia coli

Silencing Transcription from an Influenza Reverse Genetics Plasmid in E. coli Enhances Gene Stability

Reverse genetics (RG) systems have been instrumental for determining the molecular aspects of viral replication, pathogenesis, and for the development of therapeutics. Here, we demonstrate that genes encoding the influenza surface antigens hemagglutinin and neuraminidase have varying stability when cloned into a common RG plasmid and transformed into Escherichia coli. Using GFP as a reporter, we demonstrate that E. coli expresses the target genes in the RG plasmid at low levels. Incorporating lac operators or a transcriptional terminator into the plasmid reduced expression and stabilized the viral genes to varying degrees. Sandwiching the viral gene between two lac operators provided the largest contribution to stability and we confirmed the stabilization is Lac repressor-dependent and crucial for subsequent plasmid propagations in E. coli. Viruses rescued from the lac operator-stabilized plasmid displayed similar kinetics and titers to the original plasmid in two different viral backbones. Together, these results indicate that silencing transcription from the plasmid in E. coli helps to maintain the correct influenza gene sequence and that the lac operator addition does not impair virus production. It is envisaged that sandwiching DNA segments between lac operators can be used for reducing DNA segment instability in any plasmid that is propagated in E. coli which express the Lac repressor.

Sequences in the cytoplasmic tail of the gibbon ape leukemia virus envelope protein that prevent its incorporation into lentivirus vectors

Pseudotyping retrovirus and lentivirus vectors with different viral fusion proteins is a useful strategy to alter the host range of the vectors. Although lentivirus vectors are efficiently pseudotyped by Env proteins from several different subtypes of murine leukemia virus (MuLV), the related protein from gibbon ape leukemia virus (GaLV) does not form functional pseudotypes. We have determined that this arises because of an inability of GaLV Env to be incorporated into lentivirus vector particles. By exploiting the homology between the GaLV and MuLV Env proteins, we have mapped the determinants of incompatibility in the GaLV Env. Three modifications that allowed GaLV Env to pseudotype human immunodeficiency virus type 1 particles were identified: removal of the R peptide (C-terminal half of the cytoplasmic domain), replacement of the whole cytoplasmic tail with the corresponding MuLV region, and mutation of two residues upstream of the R peptide cleavage site. In addition, we have previously proposed that removal of the R peptide from MuLV Env proteins enhances their fusogenicity by transmitting a conformational change to the ectodomain of the protein (Y. Zhao et al., J. Virol. 72:5392-5398, 1998). Our analysis of chimeric MuLV/GaLV Env proteins provides further evidence in support of this model and suggests that proper Env function involves both interactions within the cytoplasmic tail and more long-range interactions between the cytoplasmic tail, the membrane-spanning region, and the ectodomain of the protein.

The C-terminal cytoplasmic tail of herpes simplex virus type 1 gE protein is phosphorylated in vivo and in vitro by cellular enzymes in the absence of other viral proteins

Herpes simplex virus 1 glycoprotein E (gE-1) is highly phosphorylated in culture cells during infection. In this report, it is shown that phosphorylation is mediated by host enzymes in human cells stably transfected with gE, in the absence of other herpesvirus products. In contrast, a tailless gE product (C terminus deletion mutant) is not phosphorylated. By using an in vitro kinase assay combined with linker-insertion mutagenesis, it is shown that casein kinase II catalyses the phosphorylation of the C-terminal domain of the protein. Also, it is demonstrated that the serine residues at positions 476 and/or 477 in the cytoplasmic portion of the protein are the major acceptors for the phosphate groups.

Construction of an overproduction vector containing the novel srp (sterically repressed) promoter

We report the design, synthesis, and evaluation of a novel Escherichia coli promoter intended for use in overproduction of proteins that are deleterious to the host. In this sterically repressed promoter (srp), the lac operator site is positioned between the -10 and -35 elements, where it can interfere sterically with RNA polymerase and thereby prevent assembly of a poised transcriptional complex. An srp-containing phagemid, pKEN1, and a tac-containing phagemid, pHN1, which has been widely used in protein overproduction but is often unstable, are compared with respect to levels of uninduced and induced protein expression. The level of uninduced protein synthesis by the srp promoter in vivo is approximately 50% of that observed with tac, whereas the levels of induced protein synthesis with the 2 vectors are approximately equal. A remarkable increase in stability of overproduction and growth was observed when the toxic Ada protein was overproduced in pKEN1, demonstrating the potential utility of this vector in overproducing toxic proteins.

Expression of a functional neisserial fbp gene in Escherichia coli

The ability to acquire iron from a human host is a major determinant in the pathogenesis of Neisseria gonorrhoeae and Neisseria meningitidis. Pathogenic Neisseria spp. do not synthesize siderophores and instead express a receptor-mediated, high-affinity iron acquisition system in the iron-restricted environment of its host. A ferric-iron-binding protein (Fbp) of Neisseria spp. is also iron-regulated and may play a central role in this novel iron-uptake system. To define the physical properties of Fbp further, we used polymerase chain reaction to synthesize DNA fragments containing the fbp structural gene with and without the sequence encoding the Fbp leader peptide. These fragments were ligated into pUC13 to create in-frame fusions with the alpha peptide of lacZ. The expression of Fbp was under the control of the lacZ promoter. Both fusion clones produced Fbp in large amounts, facilitating the purification of quantities of Fbp sufficient for elucidating the biochemical, immunologic, and functional properties of this protein.

The pathway and targeting signal for delivery of the integral membrane glycoprotein LEP100 to lysosomes

A complete set of chimeras was made between the lysosomal membrane glycoprotein LEP100 and the plasma membrane-directed vesicular stomatitis virus G protein, combining a glycosylated lumenal or ectodomain, a single transmembrane domain, and a cytosolic carboxyl-terminal domain. These chimeras, the parent molecules, and a truncated form of LEP100 lacking the transmembrane and cytosolic domains were expressed in mouse L cells. Only LEP100 and chimeras that included the cytosolic 11 amino acid carboxyl terminus of LEP100 were targeted to lysosomes. The other chimeras accumulated in the plasma membrane, and truncated LEP100 was secreted. Chimeras that included the extracellular domain of vesicular stomatitis G protein and the carboxyl terminus of LEP100 were targeted to lysosomes and very rapidly degraded. Therefore, in chimera-expressing cells, virtually all the chimeric molecules were newly synthesized and still in the biosynthesis and lysosomal targeting pathways. The behavior of one of these chimeras was studied in detail. After its processing in the Golgi apparatus, the chimera entered the plasma membrane/endosome compartment and rapidly cycled between the plasma membrane and endosomes before going to lysosomes. In pulse-expression experiments, a large population of chimeric molecules was observed to appear transiently in the plasma membrane by immunofluorescence microscopy. Soon after protein synthesis was inhibited, this surface population disappeared. When lysosomal proteolysis was inhibited, chimeric molecules accumulated in lysosomes. These data suggest that the plasma membrane/early endosome compartment is on the pathway to the lysosomal membrane. This explains why mutations that block endocytosis result in the accumulation of lysosomal membrane proteins in the plasma membrane.

Alkaline phosphatase fusions to the respiratory syncytial virus F protein as an approach to analyze its membrane topology

Manoil and Beckwith (1985) have constructed a transposon, TnphoA, that permits the generation of hybrid proteins composed of alkaline phosphatase (AP) lacking its signal peptide fused to amino-terminal sequences of other proteins. This transposon has been used to localize export signals and analyze membrane topology of bacterial proteins. We have applied this approach to the membrane fusion protein (F) of respiratory syncytial virus (RSV). The transposon TnphoA and a plasmid directing bacterial expression of the F gene were used to construct F-AP hybrids. These hybrids yielded AP activity, indicating the presence of viral sequences that promoted protein transport through the cytoplasmic membrane. Sequence analysis showed that TnphoA was inserted at four different positions within the F1 subunit. Deletion of the hydrophobic F1 amino-terminus (fusion-related domain) resulted in AP transport to the periplasm, suggesting that the hydrophobic amino-terminus of the F2 subunit is sufficient to promote protein export. Some hybrids were apparently cleaved at or near the F2/F1 junction. The periplasmic localization of an uncleaved hybrid strongly suggested that the fusion-related domain of the F protein, when in the uncleaved F0 precursor, can be moved across the bacterial cytoplasmic membrane. Although these results apply to the recombinant F protein, they agree with the presumed signal sequence and membrane topology of the native F glycoprotein. Thus, this method may be useful in determining membrane topology and in localizing important domains of viral proteins.

Induction of complement-dependent and -independent neutralizing antibodies by recombinant-derived human cytomegalovirus gp55-116 (gB)

The human cytomegalovirus (HCMV) envelope glycoprotein complex gp55-116 was expressed in both Escherichia coli and cells infected with a recombinant vaccinia virus. E. coli produced a single protein of Mr 100,000 which approximated the size of the nonglycosylated gp55-116 precursor found in HCMV-infected cells. Cells infected with the recombinant vaccinia virus contained three intracellular forms of Mr 160,000, 150,000, and 55,000 which were detected by a monoclonal antibody reactive with gp55. Comparison of the immunological properties of these recombinant proteins indicated that several of the HCMV gp55-116 monoclonal antibodies and sera from patients infected with HCMV reacted with the vaccinia virus-derived proteins whereas a more restricted group of monoclonal antibodies recognized the E. coli-produced protein. Immunization of mice with either E. coli or vaccinia virus recombinant HCMV gp55-116 resulted in production of virus-neutralizing antibodies. In contrast to the almost exclusive production of complement-dependent neutralizing antibodies following immunization with recombinant vaccinia virus, the E. coli-derived protein induced complement-independent neutralizing antibodies.

New approaches to animal vaccines utilizing genetic engineering

Control of infectious diseases in livestock is an important determinant in the success of a nation's effort to efficiently meet its need for animal products. Genetic engineering offers many new options in the design of animal vaccines. Monoclonal antibodies, DNA cloning, recombination, and transfection are examples of techniques that facilitate innovative strategies in antigen identification, production, and delivery. This article reviews the use of genetic engineering in the production of vaccines directed against foot-and-mouth disease virus and other important pathogens of animals. The advantages and disadvantages of vaccines produced through the use of genetic engineering are discussed.

Regulated expression of Sindbis and vesicular stomatitis virus glycoproteins in Saccharomyces cerevisiae

cDNAs encoding either the structural proteins (capsid and glycoproteins E1 and E2) of Sindbis virus or the glycoprotein of vesicular stomatitis virus (VSV) were fused to the Saccharomyces cerevisiae galactokinase gene (GAL1) promoter and inserted into a yeast shuttle vector. After addition of galactose to yeast transformed with this vector, 2.5-3% of total yeast protein synthesis was detected as virus proteins by specific anti-virus protein antibodies. In cells containing the Sindbis virus structural genes, the virus capsid protein was effectively released from the nascent polypeptide and two endoglycosidase H-sensitive glycoproteins were produced. One of these was identical in its gel mobility to E1 and the other appeared to be p62, a precursor to E2. A low level of E1 protein was detected on the cell's surface membranes. A single molecular weight species of glycosylated VSV glycoprotein was produced and half of the total protein could be detected at the surface membranes of yeast. Addition of long mannose chains and acylation of the virus proteins with fatty acids were not observed. Formation of virus proteins was also examined in yeast secretory mutants; one of these (sec53) failed to glycosylate the virus proteins.

Expression of the polyoma middle-size T antigen in Escherichia coli

We constructed a plasmid encoding a hybrid protein, consisting of the N-terminal signal sequence of the major outer membrane lipoprotein (lpp) of Serratia marcescens joined to the polyoma middle-size T antigen (mT antigen). The hybrid protein expressed under the control of a lpp-lac hybrid promoter was synthesized at levels up to 5% of newly synthesized protein and could be accumulated in Escherichia coli strains carrying the Cap R mutation. The mT antigen produced in E. coli was precipitated by polyoma antitumor serum, and by serum directed against a synthetic peptide corresponding to the C terminus of the authentic mT antigen. The protein was secreted into the periplasmic space, from which it could be released by osmotic shock. The bacterial mT antigen had no detectable associated protein kinase activity.

Expression of the pilin gene from Bacteroides nodosus in Escherichia coli

Bacterial plasmids that direct the expression in Escherichia coli of the pilin of Bacteroides nodosus were constructed. The quantity of pilin produced was greater than that of the pilin synthesized by B. nodosus, but no surface structural pili were present; pilin was found associated with the inner membrane of E. coli. Vaccination of sheep with E. coli containing pilin elicited increases in agglutinating and enzyme-linked immunosorbent assay antibody titers, which in turn were lower than the titers in sheep immunized with pilin from B. nodosus. The E. coli-produced pilin vaccine initially appeared to delay the progression of infection in immunized sheep after a challenge with virulent homologous B. nodosus, but at a later time the severity of foot rot was similar to that in sheep vaccinated with a placebo.

Organization and expression of genes responsible for type 1 piliation in Escherichia coli

The genetic organization of a segment of recombinant DNA conferring the capacity of synthesize E. coli type 1 pili was examined. This 11.2-kilobase (kb) segment of DNA, derived from a clinical isolate, conferred a piliated phenotype (Pil+) on a nonpiliated (Pil-) strain of E. coli K-12 that lacked DNA homologous to the 11.2-kb region. Insertional mutagenesis, deletion mutagenesis, and subcloning of various regions of the 11.2-kb fragment allowed the localization of five genes, each encoding a polypeptide, that were associated with pilus expression. Three gene products, 17, 86, and 30 kilodaltons (kd) in size, were involved in pilus assembly; assembly of the 17-kd structural (pilin) protein into pili was not seen in mutants lacking either the 86- or 30-kd proteins, but pilin synthesis and proteolytic processing were not affected. The fourth polypeptide, 23 kd in size, appeared to be involved in the regulation of pilus expression because mutants lacking this protein exhibited a 40-fold increase in the amount of pilin antigen per cell. The last protein, 14 kd in size, was not associated with piliation by genetic criteria; however, the 14-kd protein was immunoprecipitated with pili, suggesting an association with pili or immunological cross-reactivity with pilin. Immunoprecipitates of minicell transcription translation products revealed that pilus polymerization was taking place in minicells. This may facilitate the study of the molecular steps in pilus biosynthesis and, as a consequence, provide clues to the assembly of supramolecular structures in general.

Mutations not altering the symmetrical sequences in the trp operator yield a constitutive phenotype

An E. coli trp promoter operator mutant was constructed, having two base pair alterations at position -4 and -1 relative to the transcription initiation site (+1). Expression of chloramphenicol acetyltransferase gene under this trp promoter operator suggests that it is almost fully constitutive. This trp Oc in vitro derived mutant differs from previously isolated Oc mutants in that its twofold symmetry sequence is identical to that of the wild type trp operator. The base substitution in the operator does not affect the functionality of the trp promoter. The trp Oc promoter DNA fragment is engineered so that it can be manipulated conveniently for efficient expression of various genes in E. coli.

The influence of messenger RNA secondary structure on expression of an immunoglobulin heavy chain in Escherichia coli

A gene for murine mu heavy chain immunoglobulin has been inserted into a bacterial expression plasmid containing the Escherichia coli trp promoter and ribosome binding site. A low level expression of mu protein was detected. Secondary structure analysis showed the presence of a hairpin loop burying the mu initiation codon. Alteration of secondary structure at this site by oligonucleotide replacement mutagenesis revealed a correlation between mu expression levels and accessibility of the ribosome binding site. Abolition of secondary structure increased mu protein expression over ninety-fold, to a level approximately equal to that of a trpE -mu fusion protein using the native trpE ribosome binding site.

Use of the Escherichia coli lac repressor and operator to control gene expression in Bacillus subtilis

The Escherichia coli lac operator has been placed on the 3' side of the promoter for the penicillinase gene of Bacillus licheniformis, creating a hybrid promoter controllable by the E. coli lac repressor. The E. coli lac repressor gene has been placed under the control of a promoter and ribosome-binding site that allows expression in Bacillus subtilis. When the penicillinase gene that contains the lac operator is expressed in B. subtilis on a plasmid that also produces the lac repressor, the expression of the penicillinase gene can be modulated by isopropyl beta-D-thiogalactoside (IPTG), an inducer of the lac operon in E. coli. A similar system was constructed from a promoter of the B. subtilis phage SPO-1 and the leukocyte interferon A gene, which allowed the controlled expression of interferon in B. subtilis. These two examples show that a functional control system can be introduced into B. subtilis from E. coli.

Detection of antibodies to herpes simplex virus with a continuous cell line expressing cloned glycoprotein D

The gene for glycoprotein D of herpes simplex virus type 1 (HSV-1) was expressed in stable mammalian cell lines. Glycoprotein D produced in these cells has a number of antigenic determinants in common with the native glycoprotein. Cell lines expressing glycoprotein D were used in an enzyme-linked immunosorbent assay to detect human antibodies to glycoprotein D. This strategy should prove useful in determining the extent to which the immune response to HSV-1 is directed toward glycoprotein D.

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.

Genetics of digalactoside-binding adhesin from a uropathogenic Escherichia coli strain

The uropathogenic strain Escherichia coli J96 mediates mannose-resistant hemagglutination owing to production of a digalactoside-binding adhesin. A cosmid clone from this strain has been isolated that, when harbored in E. coli K-12, expressed Pap pili and this adhesin (R. Hull et al., Infect. Immun. 33:933-938, 1981). By transposon mutagenesis and by the construction of a number of hybrid plasmid derivatives, we have demonstrated that about 8.5 kilobases of DNA is required to generate a mannose-resistant hemagglutination-positive phenotype in E. coli K-12 strain P678-54. The structural gene for the Pap pili monomer, papA, has been identified and mapped close to the promotor-proximal end of the Pap operon. Although strain P678-54 that harbored a Tn5 insertion within papA showed a mannose-resistant hemagglutination-positive phenotype, it was negative in a competitive enzyme-linked immunosorbent assay with anti-Pap pilus serum. This could mean that a Pap adhesin is encoded by a region on the Pap operon that is distinct from papA.

Direct expression of hepatitis B surface antigen gene in E. coli

A 809 bp Sau 3A - Hpa I fragment containing a complete HBsAg gene and fragments 744 bp Hinc II - Hpa I and 712 bp Xba I - Hpa I containing a truncated HBsAg gene lacking the sequence encoding the NH2-terminal hydrophobic domain were prepared from a composite plasmid pHBV933 containing the 3.2 kb Eco RI DNA fragment of the entire HBV/adw genome and inserted into an expression vector pTRP801 to give plasmids pTRP SS-6, pTRP SS-39, and pTRP SS-50, respectively. The growth of a recombinant having pTRP SS-6 was greatly inhibited and the transformant expressed a low level of HBsAg, which is reactive to human anti-HBsAg antibody. Interestingly, the growth of transformants harbouring pTRP SS-39 and pTRP SS-50 was not inhibited and these transformants expressed a considerable level of the HBsAg. Minicells harbouring pTRP SS-6, pTRP SS-39, and pTRP SS-50 formed specific polypeptides of about 24 K, 23 K, and 22 K daltons, respectively.

Construction of a synthetic messenger RNA encoding a membrane protein

We have synthesized microgram quantities of a functional eucaryotic mRNA by in vitro transcription. For this purpose, we constructed a plasmid in which the Escherichia coli lactose promoter was 5' to the vesicular stomatitis virus (VSV) G protein gene (Rose, J. K., and C. J. Gallione, 1981, J. Virol., 39:519-528). This DNA served as the template in an in vitro transcription reaction utilizing E. coli RNA polymerase. The RNA product was capped using the vaccinia guanylyltransferase. A typical preparation of the synthetic G mRNA was equivalent to the amount of G mRNA that can be isolated from approximately 10(8) VSV-infected cells. This synthetic mRNA was translated by a wheat germ extract in the presence of microsomes, producing a polypeptide that was indistinguishable from G protein in its size, antigenicity, degree of glycosylation, and its membrane insertion. This technique should aid in identifying features needed by proteins for insertion into membranes.

Rabies virus glycoprotein analogs: biosynthesis in Escherichia coli

The surface of rabies virus is composed of an approximately 60,000 dalton glycoprotein, in which most of the antigenic and immunogenic determinants of the virus reside. We have constructed plasmids for the direct expression in Escherichia coli of the mature full length rabies glycoprotein gene and also for the expression of a glycoprotein gene which has been truncated to exclude the coding region for a hydrophobic, possibly transmembrane, domain of the protein. Escherichia coli harboring the plasmids synthesize analog proteins which conform by several biochemical and antigenic criteria to rabies glycoprotein.

The purification of M13 procoat, a membrane protein precursor

Many membrane proteins and most secreted proteins are initially made as precursors with an N-terminal leader sequence. We now report the isolation of M13 procoat, the precursor of the membrane-bound form of M13 coat protein. There are 40 000 copies of M13 procoat protein/cell during M13 amber 7 virus infection. Purified procoat is quantitatively cleaved by isolated leader peptidase to yield mature-length coat protein. Rabbit antibodies to M13 procoat will precipitate procoat but not coat, suggesting that the antibody molecules are specifically recognizing the leader sequence or the conformation which it induces in the whole procoat molecule.