Influenza antigenic determinants are expressed from haemagglutinin genes cloned in Escherichia coli

The specific pathogen-free human: a new frontier in oral infectious disease research

The indigenous flora acts as a deterrent to the establishment of some pathogenic species. We propose that advances in oral health research will lead to control of oral infections by altering the indigenous microflora to create a specific pathogen-free human. Investigations of important endogenous and exogenous factors which affect the oral flora and the interactions among these parameters, in health and disease, will have to be undertaken for this goal to be achieved. Several approaches to produce a specific pathogen-free human include: (1) introduction of individual or collective moieties which inhibit detrimental interactions on a genetic and molecular level; (2) genetic modification of salivary flow and protein composition by use of transgenic techniques; (3) therapeutic replacement with altered bacterial strains; (4) alteration of host immune responses to produce specific isotype immunity at the most appropriate time in the ontogeny of the oral environment; (5) production of isotype and/or antigen-specific regulatory molecules at the most appropriate time in development; (6) use of synthetic vaccines; (7) genetic alteration or replacement of cells with defective protective capabilities; and (8) use of anti-idiotype vaccines.

Involvement of the ntrA gene product in the anaerobic metabolism of Escherichia coli

The ntr A gene product, required for expression of genes involved in nitrogen fixation (nif) and regulation (ntr), was shown to be necessary for the expression of the two enzymes of the anaerobically inducible formate hydrogenlyase (FHL) pathway, formate dehydrogenase (FDHH) and hydrogenase isoenzyme 3. Consistent with this finding, the gene encoding the selenopolypeptide (fdhF) of FDHH was shown to have a nif consensus promoter. The levels of six other anaerobically inducible enzymes were examined and found to be ntrA independent. Significantly, these latter six enzymes are dependent upon the fnr gene product for their expression while FDHH and hydrogenase 3 are fnr independent. These findings indicate that there are at least two classes of anaerobically regulated promoters: one class which is ntrA dependent and fnr independent and a second class which is fnr dependent and ntr A independent.

Expression of the human apolipoprotein AI gene fused to the E. coli gene for beta-galactosidase

The human apoAI gene was expressed in E. coli by in-frame fusion to a modified beta-galactosidase gene present in plasmid pUR291. The fused beta-galactosidase-apoAI gene product was expressed at a high level and was recognized by an anti-human apoAI antiserum. Besides the fused protein, at least one degradation product having an Mr similar to that of beta-galactosidase was present in high amounts in bacterial extracts. These results and those of a pulse-chase experiment indicate that degradation took place only in the apoAI moiety of the chimeric protein.

Expression of a wheat alpha-amylase gene in Escherichia coli: recognition of the translational initiation site and the signal peptide

Transcription of a full-length cDNA clone of wheat alpha-amylase using a lac promoter in Escherichia coli results in synthesis of a precursor alpha-amylase polypeptide of the correct size, indicating that translation initiates correctly. Recognition of the plant translational initiation site by E. coli ribosomes is 15-20% as efficient as the ribosome-binding site of the beta-lactamase gene when it is fused to alpha-amylase. The alpha-amylase signal peptide is recognised in E. coli resulting in secretion of the enzyme into the periplasmic space; deletion of the signal peptide prevents secretion. Replacement of the alpha-amylase signal peptide with a beta-lactamase signal peptide also enables the bacterial cell to secrete the enzyme. The presence of the beta-lactamase and the alpha-amylase signal peptides in tandem results in secretion of the enzyme and removal of both signal peptides.

Biological and immunological properties of haemagglutinin and neuraminidase expressed from cloned cDNAs in prokaryotic and eukaryotic cells

To study the biological and immunological properties of influenza virus surface glycoproteins, cDNA copies of the haemagglutinin (HA) and the neuraminidase (NA) genes of A/WSN/33 influenza virus were cloned and expressed in prokaryotic and eukaryotic cells. In Escherichia coli, maximum expression of HA is obtained only as a fusion protein in which the NH2-terminal portion is provided by a bacterial protein (i.e. beta gal or trpLE'). The HA expressed in bacteria (bacterial HA) is recognized by polyclonal anti-WSN antibodies but not by neutralizing monoclonal antibodies. The antibodies made against the bacterial HA bind to the detergent-treated viral HA, intact virus and live influenza infected cells, but fail to show either haemagglutination inhibition (HI) or virus neutralization. These results suggest that the three-dimensional structure as well as the antigenic epitopes of the bacterial HA are different from that of native viral HA. HA, expressed from cDNA in cultured animal cells, is shown to possess the structural features of the native viral HA. It is glycosylated, transported to the apical domain of the plasma membrane of polarized cells, causes haemadsorption and can induce cell to cell fusion at low pH after proteolytic cleavage. An attempt was made to define the structural features of HA required for sorting and directional transport by making chimeras with vesicular stomatitis virus G (VSV G) proteins either by switching the amino terminus or the carboxy terminus of HA with that of VSV G. These chimeric proteins were translocated across the rough endoplasmic reticulum (RER) but were blocked in transport between the RER and cell membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretion of Semliki Forest virus membrane glycoprotein E1 from Bacillus subtilis

The gene coding for the Semliki Forest virus (SFV) membrane protein E1 was joined to a secretion vector containing the promoter and signal sequence regions of the alpha-amylase gene from Bacillus amyloliquefaciens. To facilitate secretion, the regions coding for the N-terminal signal peptide (the 6K protein) and the C-terminal hydrophobic transmembrane domain of the E1 gene were deleted. After transformation into B. Subtilis, E1 was shown by immunoblotting to be expressed at a low level (about 0.5-1 mg/1). Contrary to what was expected, most of the E1 remained cell-associated. Deletion of a residual 7 C-terminal amino acids from the 6K region neither increased the level of expression nor significantly improved the secretion. Immunofluorescence microscopy of protoplasts prepared from B. subtilis cells expressing E1 suggested that the cell-associated E1 was located at the outer surface of the bacterial membrane. Addition of protease inhibitors to the culture medium somewhat increased the amount of extracellular E1, suggesting that proteolytic degradation of the foreign gene product may be one reason for the low level of expression. This conclusion was also supported by experiments carried out in Bacillus minicells, which indicated that the expression of the E1 gene in the absence of synthesis of bacterial proteases was about the same as that of alpha-amylase expressed from the cloned gene using the same promoter and signal sequence.

Differential expression of influenza N protein and neuraminidase antigenic determinants in Escherichia coli

Two influenza gene products of similar size and codon usage have been expressed in Escherichia coli under control of the phage lambda pR promoter. The influenza N protein (NP) was expressed in its entirety after fusion to a short (12 amino acid) segment of the lambda cro gene product and constituted about 1-2% of total soluble cell protein after induction. By contrast, constructions using the full length neuraminidase (NA) gene failed to give rise to detectable amounts of NA antigen after fusion to either the 12 amino acid Cro peptide or after fusion to bacterial beta-galactosidase (beta gal). Rather, expression of NA antigenic determinants was only achieved after deletion of coding sequences at the 3' end of the beta gal-NA fusion construct such that the encoded protein precipitated within the cell.

The impact of new technologies on vaccine development

The ability to move genetic determinants between species using in vitro gene-manipulation techniques has opened up new approaches to vaccine development. This has rapidly grown into an exciting area of research in both academic and industrial laboratories. There are numerous scientific challenges which require multidisciplinary teams to solve problems in creating new immunogens. This has challenged our existing knowledge about protein structure and conformation, microbial pathogenicity and the immune system. Recombinant-DNA techniques are invaluable as tools of analysis and antigen production. The surface of micro-organisms can also be minutely explored with the use of synthetic peptides and monoclonal antibodies. Nevertheless, these new technologies do not allow us to circumvent the need for detailed understanding of pathogens and the disease process. What is apparent from the work carried out so far is that there are few easy answers to vaccine development and it is not realistic to expect rapid solutions to these problems. As there are many potential targets for constructing novel vaccines for both human and animal diseases, it is helpful to establish some priorities. There is a tendency to look at the existing effective vaccines and simply direct research at producing them more economically or with enhanced safety and stability. The advantage of this approach is that considerable background work will have already been carried out establishing the basis for the application of recombinant DNA techniques. However, this can also lead to conflicts (often within the same institute or company) between the new and old technologies. This could be to the detriment of the new technologies which are still only partly developed and may not be good enough yet to compete with existing vaccines in cost or efficacy. The more ambitious, and eventually more rewarding, approach is to attempt to develop new vaccines where none had existed before. There is a vast untapped market, especially in the parasitic diseases, but the scientific problems may be considerable and much more background work is likely to be necessary. Indeed, most of the work in this area is more accurately referred to as basic research rather than vaccine development as totally new, effective vaccines are still some way off. Having directed research towards a specific organism or disease there are still many options available as to the scientific strategy to adopt. As discussed in this review it may be possible to consider subunits, synthetic antigens and live (attenuated or heterologous) organisms as possible vaccines.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Effects of alterations in the translation control region on bacterial gene expression: use of cat gene constructs transcribed from the lac promoter as a model system

The region controlling translation of the cat gene, which codes for chloramphenicol acetyltransferase, has been varied structurally in a series of plasmids that place the gene under control of the lac promoter. These plasmid constructs have enabled study of the structural features that affect the efficiency of mRNA translation. Altering the potential for secondary structure formation within the translation control region caused a tenfold variation in the synthesis of CAT enzyme, whereas varying the distance between the Shine-Dalgarno sequence (SD) and the translation start codon from 7 to 13 bases did not significantly affect the yield of CAT. If the SD was situated in a region of mRNA that is capable of base pairing, the efficiency of translation was decreased; however, the translation start codon, AUG, can initiate translation efficiently even when located in a segment capable of duplex formation. Overlapping of the cat translation control region by translation initiated upstream markedly affected initiation of translation within the cat gene: out-to-frame overlapping translation reduced CAT production by 90%; in-frame overlapping translation prevented detectable initiation of protein synthesis at the cat gene translation start codon, and yielded only fusion proteins. The enzymatic activity of such proteins was influenced by the length of the adventitious peptide segment added to the amino-terminus of the CAT polypeptide.

Using genetically engineered bacteria for vaccine production

We concluded from this and our earlier work that biosynthetically produced FMDV VP1-specific fusion proteins are effective vaccines. Whether this method of vaccine production can be extended to many other immunogenic proteins from other organisms is not known. Some problems that could be expected to occur with bacterially produced antigens are that the immunogenic site may not be properly exposed or the peptide sequence(s) within that site may not be able to form into the correct configuration. This could be caused by hydrophobic or hydrophilic interactions in the fusion protein that do not occur in the protein at the virus surface. Also, the immunogenic site may require disulfide bonding to bring two distant parts of a protein or two different peptide chains into close proximity to form an antigenic site, as demonstrated by the studies of Atassi et al. for lysozyme-using synthetic peptides. In summary, the use of genetically programmed bacteria is a promising avenue to vaccine manufacture. For FMD, biosynthetic protein vaccines have significant advantages over current whole-virus technology.

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.

Efficient expression of influenza virus NS1 nonstructural proteins in Escherichia coli

RNA segment 8 of the influenza A virus genome codes for two nonstructural proteins, NS1 and NS2, for which the functions are unknown. Cloned cDNA copies of this gene from three different influenza A virus strains were inserted into an Escherichia coli plasmid expression vector, pAS1, carrying the strong regulatable lambda phage promoter, PL. After induction, the NS1 proteins were overproduced to levels of 20-25% of total cellular protein. This was surprising in that the codon composition for these eukaryotic genes is similar to that for weakly expressed proteins in E. coli. Thus, under the appropriate conditions, it appears that high level expression of genes containing a relatively large proportion of minor codons can be obtained. The NS1 protein produced in bacteria from a cloned cDNA copy of the A/PR/8/34 virus NS gene was purified to apparent homogeneity and used to generate a high-titer monospecific rabbit antiserum. Immunoprecipitation studies showed this antibody to be crossreactive against the NS1 proteins produced by several different influenza A virus strains. Immunofluorescence experiments in Madin-Darby canine kidney cells showed the NS1 proteins to be located in the nucleoplasm early in infection for all strains examined. With some of the strains, NS1-specific immunofluorescence was observed predominantly in the nucleoli later in infection. This technology can be used to obtain other viral proteins in pure form for structural, functional, and immunological studies.

Expression of Plasmodium falciparum blood-stage antigens in Escherichia coli: detection with antibodies from immune humans

Many proteins produced by blood stages of the malaria parasite Plasmodium falciparum are natural immunogens in man. As an approach to determining which of these are relevant to protective immunity we have constructed an expression library of P. falciparum cDNA sequences, cloned in Escherichia coli. The cDNA sequences were inserted into the beta-galactosidase gene of an ampicillin-resistant derivative of the temperature-sensitive lysogenic bacteriophage lambda gt11. About 5% of the resulting clones expressed P. falciparum sequences as polypeptides fused to beta-galactosidase. We have identified many clones that express P. falciparum antigens by immunological screening in situ with antibodies from immune human sera that inhibit P. falciparum growth in vitro. The antigen-positive clones contain P. falciparum cDNA sequences, as determined by hybridization. Some express polypeptides that are larger than beta-galactosidase and react both with antibodies to beta-galactosidase and with antibodies from humans immune to P. falciparum. The cloned P. falciparum antigens should facilitate new approaches to the identification of potential vaccine molecules.

Cloning and sequence of UK bovine rotavirus gene segment 7: marked sequence homology with simian rotavirus gene segment 8

The genome of the UK bovine rotavirus, which consists of eleven segments of dsRNA was polyadenylated and reverse-transcribed into cDNA. Complementary cDNA strands were annealed and the termini of the duplexes completed using DNA polymerase I. Full-length DNA copies of RNA segments 7, 8 and 9 were cloned into the Pst I site of pBR322 and a clone containing the entire gene 7 was identified and sequenced. Gene 7 is 1059 nucleotides in length and contains a single long open reading frame capable of coding for a protein of 317 amino-acids. The known gene product of segment 7 is a protein with an estimated molecular weight of 33,000 daltons. When the UK bovine rotavirus gene 7 sequence was compared with the published data for the homologous gene (segment 8) of the simian rotavirus SA11, it was found to be identical to it in size and the arrangement of the proposed coding and non-coding regions, and very similar in nucleotide sequence (88% homology). Most of the base changes are silent and the predicted amino-acid sequences are almost identical (96% homology).

Genes for catecholamine biosynthesis: cloning by expression and identification of the cDNA for rat dopamine beta-hydroxylase

mRNA for dopamine beta-hydroxylase [3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating), EC 1.14.17.1] has been partially purified from poly(A)+ mRNA isolated from a rat pheochromocytoma cell line. Shared antigenic determinants between tyrosine hydroxylase and dopamine beta-hydroxylase allowed us to obtain enriched fractions of dopamine beta-hydroxylase mRNA by immunoprecipitating translated mRNA products with tyrosine hydroxylase antisera. The enriched dopamine beta-hydroxylase mRNA was used to synthesize the corresponding cDNAs, which were then cloned in the Pst I site of pBR322. Recombinant colonies were characterized by an in situ colony immunoassay and hybrid-selected translation. In vitro translation of the mRNA selected from one recombinant clone produced a protein of 75,000 daltons that comigrated with authentic dopamine beta-hydroxylase. Partial proteolysis of both authentic dopamine beta-hydroxylase and the protein encoded by the recombinant clone produced identical peptide patterns.

Immune response to human influenza virus hemagglutinin expressed in Escherichia coli

Cloned DNA fragments coding for parts of strain WSN (H1N1) influenza virus hemagglutinin (HA) were fused to a bacterial leader DNA derived from the Escherichia coli trp operon. Fusion proteins produced consisted of 190 amino acids of trpLE' protein at the amino terminus, and HA amino acids, either 1-308, 1-396, or 1-548 (complete HA), at the carboxyl terminus. These proteins were expressed at high levels (10-20% of total protein) in E. coli starved for tryptophan. A CNBr fragment (HA1-211) was derived from HA-308. Each of the proteins was purified and used for immunizing mice and rabbits. The antibody produced was shown to bind to (i) the HA fusion proteins, (ii) detergent-treated viral HA, (iii) HA, on intact virions, and (iv) the HA on the surface of cells infected with influenza virus. This shows that the HA fusion proteins expressed in bacteria can elicit antibodies that recognize at least some determinants of the native viral HA, and probably could lead to development of an anti-influenza vaccine.

Plasmodium chabaudi antigens synthesized in an mRNA-dependent cell-free translation system

Intact RNAs were isolated from Plasmodium chabaudi growing synchronously in mice at different stages of the erythrocytic cycle. Translation of the mRNAs using rabbit reticulocyte lysate showed stage-specific patterns comparable to those observed in vivo. Many antigens of P. chabaudi are produced by translation in the rabbit reticulocyte lysate. Some other antigens are predominantly synthesized at a particular stage, indicating that the mRNA populations differ from one stage to another.

Studies on polysomes synthesizing influenza virus haemagglutinin

A fraction of polysomes synthesizing fowl plague virus (FPV) haemagglutinin (HA) was isolated from an infected chick embryo fibroblast (CEF) culture using a double immunoprecipitation assay. In an immunoprecipitate of HA-synthesizing polysomes (HA precipitate) the content of the HA polypeptide was increased with respect to the M1 + NS1 polypeptides as compared to a preparation of unprecipitated polysomes. In the HA precipitate, besides mRNA coding for HA synthesis, we have detected mRNAs corresponding to genes 1, 2 and 3 coding for high molecular weight P proteins. Studies of a cytoplasmic extract (CE) from FPV-infected CEF cultures in a sucrose density gradient revealed a fraction of polysomes with a sedimentation value of about 500S; the composition of virus-specific polypeptides and mRNA of the fraction was similar to that of the HA precipitate. It is thought that P proteins are synthesized on membrane-bound polysomes located closely to HA-synthesizing polysomes.

The construction of a synthetic Escherichia coli trp promoter and its use in the expression of a synthetic interferon gene

An 82 base pair DNA fragment has been synthesised which contains the E. coli trp promoter and operator sequences and also encodes the first Shine Dalgarno sequence of the trp operon. This DNA fragment is flanked by EcoRI and ClaI/TaqI cohesive ends and is thus easy to clone, transfer between vector systems and couple to genes to drive their expression. It has been cloned into plasmid pAT153, producing a convenient trp promoter vector. We have also joined the fragment to a synthetic IFN-alpha 1 gene, using synthetic oligonucleotides to generate a completely natural, highly efficient bacterial translation initiation signal on the promoter proximal side of the IFN gene. Plasmids carrying this construction enable E. coli cells to express IFN-alpha 1 almost constitutively and with significantly higher efficiency than from a lacUV5 promoter based system.

The molecular cloning and characterisation of cDNA coding for the alpha subunit of the acetylcholine receptor

A rare cDNA coding for most of the alpha subunit of the Torpedo nicotinic acetylcholine receptor has been cloned into bacteria. The use of a mismatched oligonucleotide primer of reverse transcriptase facilitated the design of an efficient, specific probe for recombinant bacteria. DNA sequence analysis has enabled the elucidation of a large part of the polypeptide primary sequence which is discussed in relation to its acetylcholine binding activity and the location of receptor within the plasma membrane. When used as a radioactive probe, the cloned cDNA binds specifically to a single Torpedo mRNA species of about 2350 nucleotides in length but fails to show significant cross-hybridisation with alpha subunit mRNA extracted from cat muscle.

Complete nucleotide sequence of the polymerase 3 gene of human influenza virus A/WSN/33

The complete nucleotide sequence of polymerase 3 (P3) gene of a human influenza virus (A/WSN/33) has been determined using cDNA clones except for the last 11 nucleotides which were obtained by direct RNA sequencing. The WSN P3 gene contains 2,341 nucleotides and codes for a protein of 759 amino acids (molecular weight 85,800). The WSN P3 protein, as deduced from the plus-strand DNA sequence, is basic and enriched in positively charged amino acids. In addition, it contains clusters of basic amino acids which may provide sites for the interaction of P3 protein with the capped primer, template, and/or other polymerase proteins during the transcriptive and replicative processes of influenza viral RNA.

Human influenza virus hemagglutinin is expressed in monkey cells using simian virus 40 vectors

We have cloned and expressed the hemagglutinin (HA) gene of a human influenza virus (A/WSN/33) in monkey kidney cells by linking it to deleted simian virus 40 (SV40) genomes that contain the entire early gene region, the origin of replication, and late leader sequences. The HA gene (1775 base pairs long) was originally inserted by the dG . dC tailing technique into the multicopy plasmid of Escherichia coli, pBR322, using cDNA made from viral RNA. The cloned gene was further modified by treatment with nuclease Bal 31 to remove the dG . dC tails and some of the untranslated sequences and recloned in E. coli after addition of BamHI restriction endonuclease linkers. A number of SV40 and HA recombinants (SV--HA) were constructed by inserting recloned HA DNA into the late gene region of SV40. The SV--HA recombinants, when complemented in a lytic infection of monkey cells by the helper function of SV40 early deletion mutants expressed influenza HA as detected by immunofluorescence and immunoprecipitation of in vivo-labeled proteins using either heterogeneous anti-influenza rabbit antibodies or monoclonal antibodies against HA. Furthermore, the WSN HA expressed by the SV--HA recombinants was also glycosylated and possessed the same molecular weight (approximately 70,000) as the uncleaved HA of WSN virus in monkey cells.

Identification of the protein products of the rrnC, ilv, rho region of the Escherichia coli K-12 chromosome

Two methods have been used to identify the protein products of the Escherichia coli K-12 ilv region at 84 min and the flanking rrnC (counterclockwise) and rho (clockwise) loci. First, a set of lambda dilv specialized transducing phages, including some phages that carry rho and others that carry part of rrnC, was used to infect UV irradiated cells. The proteins produced by the infecting lambda dilv phage were selectively labelled with radioactivity amino acids and identified by SDS gel electrophoresis and autoradiography. Second, restriction enzyme fragments were cloned from the lambda dilv phage into pBR322 and the plasmid specific gene products produced in maxicells were similarly identified by SDS gel electrophoresis and autoradiography. The proteins produced were correlated with specific genes and restriction enzyme fragments present in the lambda dilv phage and the pBR322 derivatives. Several ilv gene products that have previously been refractory to protein purification attempts have been identified for the first time by this technique. The presence of mutations at the ilvO site is shown to activate the cryptic ilvG gene and to result in the production of a 62,000 dalton protein. A 15,000 dalton protein of unknown function is synthesized from a DNA segment between ilv and rrnC. The rho gene was cloned from lambda dilv phage into pBR322 and shown to be dominant to a rho mutation on the host chromosome. The rho gene product and four additional proteins coded by genes near or between rho and ilv have been detected.

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

Bacterial plasmids that directed expression of the vesicular stomatitis virus glycoprotein (G-protein) gene under control of the tryptophan operon regulatory region were constructed. A plasmid directing the synthesis of a G-protein-like protein (containing the NH2-terminal segment of seven amino acids encoded by the trpE gene fused to the complete G-protein sequence lacking only its NH2-terminal methionine) could be transformed into trpR+ (repressed) but not into trpR- (derepressed) cells. This result suggested initially that derepressed synthesis of the G-protein-like protein encoded by this plasmid was lethal in Escherichia coli. Deletion of the sequence encoding the large hydrophobic segment near the COOH terminus of G-protein did not overcome this lethality. Lethality of derepressed synthesis was overcome by deletion of the G-protein gene region encoding 10 amino acids in the hydrophobic NH2-terminal domain (signal peptide). Tryptic peptide mapping demonstrated that the G-protein-like protein and some truncated proteins encoded by the plasmid contained G-protein protein sequences. Antisera to vesicular stomatitis virus precipitated the G-protein-like protein, showing that it shares antigenic determinants with the authentic G-protein protein.

Cell-surface expression of influenza haemagglutinin from a cloned DNA copy of the RNA gene

By replacing either the eight early or the late genes of SV40 with a cloned copy of the influenza virus haemagglutinin gene we have constructed recombinant viruses which, in infected cells, express large quantities of haemagglutinin. This glycoprotein, over 10(8) molecules of which are produced per cell, is identical in molecular weight to authentic influenza virus haemagglutinin, accumulates at the cell surface and displays haemabsorbing activity.

Expression of antigenic determinants of the hemagglutinin gene of a human influenza virus in Escherichia coli

Antigenic determinants of influenza virus hemagglutinin were expressed in Escherichia coli. DNA coding for presequences of hemagglutinin were removed and an ATG codon was placed before DNA coding for mature hemagglutinin. A number of expression plasmids were constructed in which various segments of this reconstructed hemagglutinin DNA were fused to DNA coding for bacterial beta-galactosidase. The fusion proteins exhibited specific binding to antiviral antibodies. This binding could be competitively inhibited by excess viral hemagglutinin, demonstrating that these fusion proteins contained antigenic determinants of hemagglutinin.

Direct immunoassay for detecting Escherichia coli colonies that contain polypeptides encoded by cloned DNA segments

We describe a simple in situ immunoassay for screening Escherichia coli colonies, to detect those that express polypeptide antigens encoded by cloned DNA segments. In the colony immunoassay that we have developed, only one antibody molecule need bind to the polypeptide molecule. Hence short fragments of coding sequences should be detectable, and problems imposed by the conformation of polypeptides "fused" to protein fragments encoded by the vector should be minimized. The method should allow the use of monoclonal antibodies, which bind to only one determinant. Colonies grown on nitrocellulose filters were lysed in situ and proteins from the lysates were blotted onto CNBr-activated filter papers. Antigens covalently bound to the CNBr paper were detected by reaction with antiserum, followed by 125I-labeled protein A from Staphylococcus aureus and autoradiography. We have used the colony immunoassay to determine what proportion of ptrpED5-1 clones containing mouse mu chain cDNA segments express mu polypeptides. Surprisingly, about 50% of the clones were positive. Because only one in six clones would be expected to contain the insert in the correct orientation and reading frame to encode a fused polypeptide, it is likely that polypeptides that initiate within the insert can be detected. A similarly high proportion of pBR322 clones containing mu cDNA were positive, and about 25% of pBR322 clones containing mouse gamma 2a chain cDNA were positive to anti-gamma 2a serum. EAch of the positive mu clones reacted with affinity-purified anti-mu antibodies but not with normal serum, and clones containing irrelevant sequences were negative. The mu cDNA segment was inserted in the correct orientation in all six clones studied, and discrete mu polypeptides corresponding in size both to fused polypeptides and internally initiated polypeptides were detected by electrophoresis of protein extracts.

[Prospects and limitations of genetic engineering]

Examples for genetic engineering are the transfer of nuclei between cells of higher animals and the introduction of heterologous DNA into bacteria by means of plasmids. The former approach will help to establish new ways in animal breeding, the latter provides bacterial cells that produce proteins of medical importance. The moral justification of related studies in man is still open, but the possible risks of gene technology can be coped with by adhering to proper safety regulations.

Expression of herpes simplex virus type I thymidine kinase gene in Escherichia coli

A herpes simplex virus type I DNA fragment containing the sequence coding for thymidine kinase was fused to the very beginning of the Escherichia coli lac Z gene in the three possible reading frames. When the thymidine kinase sequence was in the orientation fit to be transcribed from the lac promoter, functional thymidine kinase was made under lac control in all three cases. Sequences data indicate that translation reinitiation occurs at the 5' end of the thymidine kinase gene after stop signals. Two T+A-rich sequences, which may be part of eukaryotic promoters, are found in the same region.

The absence of introns within a human fibroblast interferon gene

Experiments in which immobilised restriction fragments of genomic DNA were hybridised with a cloned human fibroblast interferon cDNA indicate that the homologous chromosomal genes exist in only one basic arrangement. This is in marked contrast to recent studies by Nagata et al. (1) showing that there are at least eight gene arrangements for human leukocyte interferon. Having isolated a chromosomal human fibroblast interferon gene from a gene bank, we conclude from nucleotide sequencing studies that there is a complete absence of introns within the RNA-coding region. In view of a similar observation recently made for a human leukocyte interferon gene (1), it would appear as if interferon genes in general are unlike the vast majority of eukaryote genes in this respect.

Organization of transcriptional signals in plasmids pBR322 and pACYC184

Electron microscopic analysis of in vitro transcriptional complexes of pBR322 and pACYC184 revealed five and six major transcriptional units, respectively, in these two plasmid vectors. These units are transcribed with various efficiencies, depending upon the individual promoter strengths, which differ in pBR322 up to 10-fold. A most interesting signal arrangement was found at the beginning of the tetracycline resistance region, where two partially overlapping promoters (P1 and P2) initiate transcription crosswise in opposite directions. Whereas P2 is known to promote tetracycline resistance and to be inactivated by HindIII cleavage, P1 is able to transcribe DNA integrated at that site and probably contributes to the expression of the beta-lactamase gene in pBR322. In pACYC184, besides P1, P2, and the cat (chloramphenicol resistance) promoter (P5), two initiation sites (P3 and P4) were mapped in a region that appears to be part of insertion sequence 1. The maps of transcription signals permit a more predictable utilization of these cloning vehicles and also allow the reinterpretation of earlier cloning results.