Efficient expression of influenza virus NS1 nonstructural proteins in Escherichia coli.

Abstract

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, pASI, carrying the strong regulatable A 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.Influenza A viruses contain a genome of eight segmented single-stranded RNAs of negative polarity that, when transcribed into mRNA, code for at least 10 polypeptides (1,2). Three of these gene products (NS1, NS2, and M2) are found only in virus-infected cells. The other seven proteins are present in the virion, associated with the viral envelope (HA, NA, and Ml), or as part of the core complex (PB1, PB2, PA, and NP). The ability to obtain large quantities of these viral proteins in pure form will greatly enhance studies of the structure of these polypeptides and help to elucidate the function(s) of these gene products during the virus replication cycle.With the emergence of recombinant DNA technology, it has been possible to clone cDNA copies of the eight influenza virus genomic RNAs into Escherichia coli plasmid vectors (3). In this paper, we describe the bacterial production of the influenza virus NS1 nonstructural proteins from three different viral strains. The viral cDNA coding for the NS1 protein was inserted into a plasmid vehicle, pASl, that contains transcriptional and translational signals derived from bacteriophage A (4). Under the appropriate induction conditions, large quantities of NSL protein were produced in an E. coli host. The protein was then extracted and purified for use as an immunogen to generate a hightiter monospecific antiserum in rabbits for in vitro and in vivo studies.Immunoprecipitation studies using this antiserum showed it to be crossreactive with all strains tested, and immunofluorescence experiments re...

Regulation of a nuclear export signal by an adjacent inhibitory sequence: The effector domain of the influenza virus NS1 protein

“…Two functional domains of the NS1 protein are required for these nuclear functions: an RNA-binding domain near the amino terminus, and an effector domain in the carboxyl half of the molecule (8). Consistent with these functions, previous studies showed that the NS1 protein is predominantly localized to the nucleus both in infected cells and in cells transfected with the DNA encoding the NS1 protein (12)(13)(14)(15)(16). This nuclear localization is directed at least in part by two separate, independent NLSs in the protein (13).…”

Effects of expression of mammalian G alpha and hybrid mammalian-yeast G alpha proteins on the yeast pheromone response signal transduction pathway.

“…1) A polyclonal antiserum raised against a fusion of Gas to the N-terminal 81 residues of the influenza virus NSI protein (34) was used to detect total cellular Gas proteins by Western blot (immunoblot) (data not shown). Protein was undetectable in cells of strain DJ211-3-4 expressing pGALas.…”

Unfolding domains of recombinant fusion αα‐tropomyosin

“…Fusion-tropomyosin was prepared from full-length cDNA clones of rat striated muscle obtained from Dr. B. NadalGinard (Ruiz-Opazo & Nadal-Ginard, 1987), subcloned, and expressed in Escherichia coli using a rat striated muscle a-tropomyosin cDNA (gift of Dr. B. Nadal-Ginard; Ruiz-Opazo & Nadal- Ginard, 1987) that was cloned in pas AEH801 (Young et al, 1983) to produce a fusion protein with 80 amino acids of influenza virus NS1 on the amino terminus (Heald & Hitchcock-DeGregori, 1988;Cho et al, 1990). It was purified and renatured from GuHCl extracts as described earlier (Hitchcock-DeGregori & Varnell, 1990).…”