Recombinant Plaques Research Articles

Stability of the HSV-2 US-6 Gene in the del II, del III, CP77, and I8R-G1L Sites in Modified Vaccinia Virus Ankara After Serial Passage of Recombinant Vectors in Cells.

The modified vaccinia virus Ankara (MVA), a severely attenuated strain of vaccinia virus, is a promising vector platform for viral-vectored vaccine development because of its attributes of efficient transgene expression and safety profile, among others. Thus, transgene stability in MVA is important to assure immunogenicity and efficacy. The global GC content of the MVA genome is 33%, and GC-rich sequences containing runs of C or G nucleotides have been reported to be less stable with passage of MVA vectors in cells. The production of recombinant MVA vaccines requires a number of expansion steps in cell culture, depending on production scale. We assessed the effect of extensive passage of four recombinant MVA vectors on the stability of the GC-rich herpes simplex type 2 (HSV-2) US6 gene encoding viral glycoprotein D (gD2) inserted at four different genomic sites, including the deletion (del) II and del III sites, the CP77 gene locus (MVA_009–MVA_013) and the I8R-G1L intergenic region. Our data indicate that after 35 passages, there was a reduction in gD2 expression from del II, del III and CP77 sites. Sequencing analysis implicated US6 deletion and mutational events as responsible for the loss of gD2 expression. By contrast, 85.9% of recombinant plaques expressed gD2 from the I8R-G1L site, suggesting better accommodation of transgenes in this intergenic region. Thus, the I8R-G1L intergenic region may be more useful for transgene insertion for enhanced stability.

Application of poxvirus K3 ortholog as a positive selection marker for constructing recombinant vaccinia viruses with modified host range

Vaccinia virus is capable of replicating in a wide range of vertebrate animal cells. However, deletion of the two virus host range genes, E3L and K3L, would render replication of the virus abortive in all the cell types tested, except the cells with defective PKR and RNase L activity. By expressing different poxvirus K3 ortholog proteins in the E3L and K3L double knockout vaccinia virus, we can construct a mutant vaccinia virus with modified host range. Here, using poxvirus K3 ortholog as a positive selection marker, we developed a proof-of-concept protocol to construct recombinant vaccinia viruses expressing foreign proteins. Such a recombinant virus has a modified host range in comparison to wild-type vaccinia virus. This protocol offers the following advantages:➢Cheap: no additional selection reagent is required.➢Highly efficient: nearly all recombinant virus plaques picked would be the stable recombinant virus expressing the protein of interest.➢Rapid: starting from transfection with the recombinant DNA vector, a purified recombinant virus expressing the protein of interest could be obtained within a week.

B Virus (Macacine herpesvirus 1) Glycoprotein D Is Functional but Dispensable for Virus Entry into Macaque and Human Skin Cells.

Glycoprotein D (gD) plays an essential role in cell entry of many simplexviruses. B virus (Macacine herpesvirus 1) is closely related to herpes simplex virus 1 (HSV-1) and encodes gD, which shares more than 70% amino acid similarity with HSV-1 gD. Previously, we have demonstrated that B virus gD polyclonal antibodies were unable to neutralize B virus infectivity on epithelial cell lines, suggesting gD is not required for B virus entry into these cells. In the present study, we confirmed this finding by producing a B virus mutant, BV-ΔgDZ, in which the gD gene was replaced with a lacZ expression cassette. Recombinant plaques were selected on complementing VD60 cells expressing HSV-1 gD. Virions lacking gD were produced in Vero cells infected with BV-ΔgDZ. In contrast to HSV-1, B virus lacking gD was able to infect and form plaques on noncomplementing cell lines, including Vero, HEp-2, LLC-MK2, primary human and macaque dermal fibroblasts, and U373 human glioblastoma cells. The gD-negative BV-ΔgDZ also failed to enter entry-resistant murine B78H1 cells bearing a single gD receptor, human nectin-1, but gained the ability to enter when phenotypically supplemented with HSV-1 gD. Cell attachment and penetration rates, as well as the replication characteristics of BV-ΔgDZ in Vero cells, were almost identical to those of wild-type (wt) B virus. These observations indicate that B virus can utilize gD-independent cell entry and transmission mechanisms, in addition to generally used gD-dependent mechanisms. B virus is the only known simplexvirus that causes zoonotic infection, resulting in approximately 80% mortality in untreated humans or in lifelong persistence with the constant threat of reactivation in survivors. Here, we report that B virus lacking the gD envelope glycoprotein infects both human and monkey cells as efficiently as wild-type B virus. These data provide evidence for a novel mechanism(s) utilized by B virus to gain access to target cells. This mechanism is different from those used by its close relatives, HSV-1 and -2, where gD is a pivotal protein in the virus entry process. The possibility remains that unidentified receptors, specific for B virus, permit virus entry into target cells through gD-independent pathways. Understanding the molecular mechanisms of B virus entry may help in developing rational therapeutic strategies for the prevention and treatment of B virus infection in both macaques and humans.

An Efficient Method for Generating Poxvirus Recombinants in the Absence of Selection

The use of selectable markers (ecogpt) and selection pressures to aid in detection of poxvirus (Vaccinia, VV) recombinants has been implicated in the unintended introduction of second site mutations. We have reinvestigated the use of the helper virus system described by Scheiflinger et al. [1] and adapted by Yao and Evans [2] which produces recombinants at a high frequency in the absence of any selection, at a rate of 6–100%. Our system uses fowlpox virus (FPV) as the infectious helper virus which in infected cells provides the enzymatic apparatus for transcription and replication of a purified, transfected VV genome and for recombination with a second transfected PCR generated DNA fragment. To optimize the system, a PCR DNA fragment was generated that contained poxvirus promoter driven gfp and lacZ genes inserted within the coding sequences of the viral thymidine kinase gene. This PCR fragment was co-transfected together with VV genomic DNA. Recombinant VV was identified by plaquing the mixture on cells non-permissive for FPV and selection of green fluorescent or LacZ positive recombinant vaccinia plaques. The system was optimized using FPV permissive cells (CEF) and non-permissive cells (A549, CV-1) for both the initial infection/transfection and the subsequent selection. Up to 70% of the progeny vaccinia virus contained the gfp/LacZ insertion. In order to test for the presence of FPV/VV intertypic recombinants or other unintended mutations, recombinant wtVV (RwtVV) was regenerated from the gfp/LacZ viruses and evaluated by RFLP analysis and pathogenesis in animals. While all RwtVVs were viable in cell culture, in many of the RwtVV isolates, RFLP differences were noted and while some recombinant viruses exhibited wild type behavior in mice, a wide range of virulence indicative of unintended changes suggests that mutants created by “rescue” systems require careful analysis particularly before use for in vivo studies employing animal models.

Characterization of LORF11, a Unique Gene Common to the Three Marek's Disease Virus Serotypes

The unique open reading frame 11 (LORF11) of Marek's disease virus (MDV) is present in all three serotypes of MDV and is located in the unique long region of the MDV genome. In the serotype 1 Md5 genome, LORF11 comprises 2711 nucleotides and encodes a predicted protein of 903 amino acids. In order to study the biological function of LORF11 we deleted it from the MDV cosmid A6 by using the RecA-assisted restriction endonuclease cleavage method. The recombinant cosmid, A6DeltaLORF11, was transfected into duck embryo fibroblasts (DEF) in conjunction with parental SN5, P89, SN16, and B40 cosmid clones. Recombinant rMd5DeltaLORF11 plaques were evident at 12-13 days after transfection. Polymerase chain reaction amplification of DEF cells infected with rMd5DeltaLORF11 viruses confirmed the deletion of a 2.57-kb fragment resulting in a 296-bp fragment. Three rMd5DeltaLORF11 mutants were generated and their biological functions were studied in vitro and in vivo. In vitro growth characteristics of rMd5DeltaLORF11 viruses were similar to those of parental rMd5, indicating that LORF11 is not essential for replication in vitro. In vivo studies of rMd5DeltaLORF11 mutants showed that they were impaired in viral replication in the lymphoid organs and had 100x lower viremia than chickens infected with the parental rMd5 virus. Furthermore, rMd5-infected chickens horizontally transmitted the virus to contact controls whereas no horizontal transmission occurred in rMd5DeltaLORF11-infected chickens. Three independent deletion mutants were tested and showed the same phenotypes, so it is unlikely that the observed phenotype is because of any random mutation in the genome. Therefore the LORF11 gene of MDV is essential for normal virus replication in chickens and deletion of LORF11 renders an attenuated virus.

Synthesis of the allergen ovomucoid by a replicating Mengo virus

Interferons induced by viral infections can have powerful immuno- modulatory effects, and several epidemiologic studies have found an association between certain viral infections and reduced prevalence of allergy. We hypothesized that allergenic proteins could be synthesized by a replicating virus, and this construct could be useful as an immunomodulator. To test this hypothesis, we cloned an allergenic protein (ovomucoid [OVM]) into a murine picornavirus (Mengo virus) vector. This plasmid has a multicloning site surrounded by auto-catalytic sequences so that a foreign protein will be cleaved from viral proteins during replication. OVM sequences were cloned in the context of full-length viral genome cDNA, T7 RNA transcripts of this plasmid were transfected into HeLa cells, and recombinant virus plaques appeared on the second passage. Sequence analysis of recombinant viruses derived from individual plaques demonstrated that three viral isolates contained up to 2/3 of the OVM coding sequence, which was retained by the viruses after 5 additional passages in HeLa cells. The experiments verify the stable expression of immunoreactive OVM subunits by replicating viruses. These virus/allergen constructs could provide a tool to evaluate whether intracellular presentation of allergenic proteins in the context of a viral infection could prevent allergic sensitization upon re-challenge.

Overproduction and partial purification of the Norrie disease gene product, norrin, from a recombinant baculovirus

Abnormal vascularization of the peripheral retina and retinal detachment are common clinical characteristics of Norrie disease (ND), familial exudative vitreoretinopathy, Coats’ disease, and retinopathy of prematurity. Although little is known about the molecular basis of these diseases, studies have shown that all of these diseases are associated with mutations in the ND gene. In spite of this, little is known about norrin, its molecular mechanism of action, and its functional relationship with the development of abnormal retinal vasculature. To obtain a large quantity of norrin for structural and functional studies, we have overproduced it in insect cells. For this purpose, a cDNA fragment (869 bp) was isolated from a human retinal cDNA library by amplification and was cloned into an expression vector. The purified plasmid was co-transfected with wild-type linearized Bac-N-Blue DNA into S. frugiperda Sf21 insect cells. The recombinant virus plaques were purified and clones were selected based on the level of recombinant protein expressed in Sf21 cells infected with a purified recombinant virus. From these, a high-titer stock was generated and subsequently used to prepare a fused protein on a large scale. The protein was partially purified by the process of immobilized metal affinity chromatography and the use of ion exchange chromatography

Cloning and sequence analysis of the complementary DNA for feline preproparathyroid hormone.

To clone and sequence the cDNA for feline preproparathyroid hormone (preproPTH) and to compare that sequence with other known parathyroid hormone (PTH) sequences. Parathyroid glands from 1 healthy cat. A cDNA library was constructed in lambda phage from feline parathyroid gland mRNA and screened with a radiolabeled canine PTH probe. Positive clones were sequenced, and nucleic acid and deduced amino acid sequences were analyzed and compared with known preproPTH and PTH sequences. Screening of approximately 2 X 10(5) recombinant plaques revealed 3 that hybridized with the canine PTH probe; 2 clones comprised the complete sequence for feline preproPTH. Feline preproPTH cDNA consisted of a 63-base pair (bp) 5'-untranslated region (UTR), a 348-bp coding region, and a 326-bp 3'-UTR. The coding region encoded a 115-amino acid peptide. Mature feline PTH consisted of 84 amino acids. Amino acid sequence analysis revealed that feline PTH was > 83% identical to canine, bovine, swine, equine, human, and macaque PTH and 69, 71, and 44% identical to mouse, rat, and chicken PTH, respectively. Within the region responsible for hormonal activity (amino acids 1 to 34), feline PTH was > 79% identical to other mammalian PTH sequences and 64% identical to the chicken sequence. The amino acid sequence of PTH is conserved among mammalian species. Knowledge of the cDNA sequence for feline PTH may be useful to investigate disturbances of calcium metabolism and alterations in PTH expression in cats.

Identification of two Mycobacterium avium subspecies paratuberculosis gene products differentially recognised by sera from rabbits immunised with live mycobacteria but not heat-killed mycobacteria.

The investigation of environmentally regulated proteins has led to a better understanding of host-pathogen interactions and identified novel vaccine candidate antigens for several bacterial pathogens. In an effort to identify such proteins in Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis), a genomic expression library was differentially screened with sera from rabbits that had been immunised with live M. paratuberculosis (alpha-live) as well as sera from rabbits immunised with heat-killed M. paratuberculosis (alpha-killed). These experiments identified seven recombinant plaques that were uniquely recognised by the alpha-live sera. Sequence data showed that five of these clones overlapped with each other and contained a common open-reading frame encoding a 25-kDa protein, termed Csp1. The 25-kDa antigen shows weak similarity to a secreted Corynebacterium glutamicum protein. The remaining two clones overlapped with each other and contained two partial open-reading frames, both encoding proteins with strong homology to polyketide synthase from various species of mycobacteria. Antisera were produced against a peptide of the polyketide synthase gene product designated Pks7. Csp1-specific antibodies were affinity purified from the alpha-live sera. These purified antibodies demonstrated that Csp1 was present within infected macrophages. Collectively, these data identify novel M. paratuberculosis antigens that may be important in pathogenesis.

Characterization of the myxoma virus M118L protein: a novel essential poxvirus IMV-associated protein.

Myxoma M118L ORF has the capacity to encode a 76 amino acid protein that is highly conserved in other vertebrate poxviruses including vaccinia (A30L), molluscum contagiosum (MC136L), yaba tumour virus (D13L) and fowlpox virus (FPV 194). The time course analysis by Western blotting using M118L antibody showed that the M118L ORF is expressed as a typical poxvirus late gene. The M118L protein can be detected in both the virus infected cytosolic and membrane fractions, even though the M118L protein does not possess a predicted transmembrane domain. The protein was found to be associated with the sucrose gradient purified myxoma intracellular mature virus (IMV) as determined by Western blotting with M118L antibody. Furthermore, the M118L protein associated with the IMV can be surface labeled with water-soluble biotin and is released from the purified IMV with treatment of nonionic detergent NP-40, indicating that the M118L protein is associated with the outer membrane of myxoma IMV. Unexpectedly, an IMV-associated M118L protein isoform was observed to bind tightly to Streptavidin beads, unlike the six other detectable myxoma IMV surface proteins, suggesting an unusual post-translational modification, such as biotinylation. Extensive attempts to generate the M118L deletion mutant using standard homologous recombination technique with E. coli gpt gene as a positive selection marker were unsuccessful. Although PCR analysis clearly indicated the presence of the correctly targeted M118L deletion mutants in mixed recombinant virus plaques selected with mycophenolic acid (MPA), repeated passages and plaquing failed to segregate the pure M118L deletion mutant from either single crossover recombinants or regenerated wild type parental viruses. Taken together, our data strongly indicate that the M118L is a novel poxvirus IMV associated protein that is essential for virus viability.

Construction of adenoviral vectors.

Recombinant adenovirus vectors have proven to be useful tools in facilitating gene transfer. Construction of such vectors requires a knowledge of the adenovirus genome structure and its life cycle. A commonly used recombinant adenovirus involves deletion of the E1 region; such a recombinant is traditionally produced by overlap recombination after cotransfection of 293 cells with a plasmid shuttle vector and a large right-end restriction fragment of viral DNA. The shuttle vector contains a cassette for a transgene placed in region E1 and flanking sequences from adenovirus for recombination. Normally, a high background of parental virus results because of the difficulty in separating right-end restriction fragment length DNA from uncut DNA. This paper describes a negative selection based on the traditional cotransfection method using viral DNA from an E1-deleted adenoviral recombinant that expresses green fluorescent protein (GFP). In situ fluorescent microscopy is used to distinguish the recombinant plaques (white or nonfluorescent) from the parental virus plaques (green or fluorescent). In addition, this system allows for the detection of contaminating parental virus at later stages when production lots of the recombinant vector are being made.

Construction of adenoviral vectors.

Recombinant adenovirus vectors have proven to be useful tools in facilitating gene transfer. Construction of such vectors requires a knowledge of the adenovirus genome structure and its life cycle. A commonly used recombinant adenovirus involves deletion of the E1 region; such a recombinant is traditionally produced by overlap recombination after contransfection of 293 cells with a plasmid shuttle vector and a large right-end restriction fragment of viral DNA. The shuttle vector contains a cassette for a transgene placed in region E1 and flanking sequences from adenovirus for recombination. Normally, a high background of parental virus results because of the difficulty in separating right-end restriction fragment length DNA from uncut DNA. This paper describes a negative selection based on the traditional cotransfection method using viral DNA from an E1-deleted adenoviral recombinant that expresses green fluorescent protein (GFP). In situ fluorescent microscopy is used to distinguish the recombinant plaques (white or nonfluorescent) from the parental virus plaques (green or fluorescent). In addition, this system allows for the detection of contaminating parental virus at later stages when production lots of the recombinant vector are being made.

Incorporation of the green fluorescent protein into the herpes simplex virus type 1 capsid.

The herpes simplex virus type 1 (HSV-1) UL35 open reading frame (ORF) encodes a 12-kDa capsid protein designated VP26. VP26 is located on the outer surface of the capsid specifically on the tips of the hexons that constitute the capsid shell. The bioluminescent jellyfish (Aequorea victoria) green fluorescent protein (GFP) was fused in frame with the UL35 ORF to generate a VP26-GFP fusion protein. This fusion protein was fluorescent and localized to distinct regions within the nuclei of transfected cells following infection with wild-type virus. The VP26-GFP marker was introduced into the HSV-1 (KOS) genome resulting in recombinant plaques that were fluorescent. A virus, designated K26GFP, was isolated and purified and was shown to grow as well as the wild-type virus in cell culture. An analysis of the intranuclear capsids formed in K26GFP-infected cells revealed that the fusion protein was incorporated into A, B, and C capsids. Furthermore, the fusion protein incorporated into the virion particle was fluorescent as judged by fluorescence-activated cell sorter (FACS) analysis of infected cells in the absence of de novo protein synthesis. Cells infected with K26GFP exhibited a punctate nuclear fluorescence at early times in the replication cycle. At later times during infection a generalized cytoplasmic and nuclear fluorescence, including fluorescence at the cell membranes, was observed, confirming visually that the fusion protein was incorporated into intranuclear capsids and mature virions.

High throughput method for creating and screening recombinant adenoviruses.

Replication defective adenoviruses are being considered as vectors in therapeutic applications of gene therapy, as well as research tools in studying gene function. Important to their successful utilization is the development of techniques to isolate new recombinants quickly, which are not contaminated with wild-type virus. We describe a modification of the traditional technique to create recombinant adenoviruses in which a 5' plasmid containing vector sequence is cotransfected into 293 cells with viral DNA. In our protocol, the viral DNA is derived from the 3' portion of an E1-deleted recombinant that expresses the green fluorescent protein. Visualization of the cotransfection by fluorescent microscopy distinguishes recombinant plaques (nonfluorescent or 'white plaque') from background plaques (green fluorescent or 'green plaque'). Using this approach we have been able to increase substantially the success and throughput for creating new recombinants while minimizing contamination. This has been used to isolate adenoviral vectors deleted in a number of essential genes.

Expression of feline recombinant interferon-γ in baculovirus and demonstration of biological activity

We have previously reported the cloning of the coding sequence for feline-specific interferon-γ. Here, we describe the expression of this sequence in a baculovirus system and demonstrate the biological activity of the recombinant protein. The coding sequence for feline interferon was directionally cloned into the baculovirus transfer vector pAcCL29-1. Transfer vector and linearized wild-type AcMNPV (BacPAK6) were used to co-transfect Sf9 cells by calcium phosphate co-precipitation. Subsequently, wild-type and recombinant viruses were separated by plaque assay. Recombinant plaques were expanded and a master stock of virus is produced. Production of biologically active interferon-gamma from infected Sf9 cells was demonstrated using a standard cytopathic effect reduction assay, utilising vesicular stomatitis virus (VSV), and an MHC class II induction assay.

Characterization of Recombinant Vaccinia Viruses and Their Products

After a recombinant vaccinia virus is made, its DNA and protein products can be analyzed in several ways. Protocols are provided in this unit for identification of the recombinant virus by PCR (with verification of correct insertion of the DNA by Southern blotting) and by dot-blot hybridization. Also, when antibodies are available, protein expression can be analyzed by immunological methods detailed here such as dot blotting with an antibody, immunoblotting and/or immunoprecipitation. In addition, immunostaining can be used for identification of recombinant plaques as well as for determination of the purity of a recombinant virus stock. All of the protocols in this unit can be used for characterization of modified vaccinia virus Ankara (MVA) recombinant viruses.

Characterization of Recombinant Vaccinia Viruses and Their Products

After a recombinant vaccinia virus is made, its DNA and protein products can be analyzed in several ways. Protocols are provided in this unit for identification of the recombinant virus by PCR (with verification of correct insertion of the DNA by Southern blotting) and by dot-blot hybridization. Also, when antibodies are available, protein expression can be analyzed by immunological methods detailed here such as dot blotting with an antibody, immunoblotting and/or immunoprecipitation. In addition, immunostaining can be used for identification of recombinant plaques as well as for determination of the purity of a recombinant virus stock. All of the protocols in this unit can be used for characterization of modified vaccinia virus Ankara (MVA) recombinant viruses.

Cloning and characterization of the 5′ flanking region of human ATP-citrate lyase gene

Two phage clones, λhgACL21 and λhgACL28, harboring the 5′ flanking region of human ATP-citrate lyase (ACL) gene were identified by screening about 1.5×10 6 recombinant plaques from the λEMBL3-human placental genomic DNA library. The 5′ flanking region of ACL had the CAAT box on −92 bp from the transcription initiation site (+1), however, the TATA box was not found. The primer extension and rapid amplification of cDNA end showed that mRNA is transcribed at a thymine extending 12 bp upstream of the reported cDNA end. The sequences of 5′ flanking region in 1.5 kb size of human ACL showed 60% homology with those of rat; however, no homology was found in the exon 1 and intron 1 region. Several consensus sequences, including four Sp1 binding sites, were found in the 5′ flanking region of this gene. The promoter activity was assayed by transfecting the 3′ or 5′ deletion clones of ACL-chloramphenicol acetyl transferase (CAT) plasmid into PLC/PRF5 cells. The clone that contains the part of the first intron sequences from −659 to +440 bp showed the highest CAT activity in the transient transfection assay. High promoter activities were maintained until the transcription initiation site was removed. It is suggested that the sequences from −213 to +12 which contain three Sp1-binding sequences, CAAT box, and the transcription initiation site were necessary as a mean of for exerting the basal promoter activity of ACL gene.

Analysis of a randomly assorted cDNA library from BW 5147 lymphoid cells. Frequency estimates based on computer aided concatenation matching of 2D gel polypeptide products

A cDNA library was divided into 291 sectors of low complexity, 800–1000 recombinant phage plaques per sector. Aliquots of DNA from sectors prepared from high titer phage were subjected to in vitro transcription using T7 polymerase and thereafter RNA was translated in a cell-free rabbit reticulocyte system in the presence of [ 35S] methionine. The resulting polypeptides were separated by 2D gel electrophoresis. Radiofluorographs of the gels prepared from 10 sectors were subjected to scanning and image analysis. A multilevel spot matching procedure was employed allowing us to recognise spot occurrence in the 10 sectors. The number of detected polypeptide spots per sector varied between 147 and 325. Overall, 1082 different spots were counted totalling 1983 spots considering multiple entries. The distribution of the spots and the frequency distribution of the RNA population among the 10 sectors are shown. The highest detected frequency is 10 −2, while one half of the RNA molecular species are present at a frequency of 10 −3 or lower.

Cloning, expression and toxicity of a mosquitocidal toxin gene of Bacillus thuringiensis subsp. medellin.

Bacillus thuringiensis (Bt) subsp. medellin (Btmed) produces parasporal crystalline inclusions which are toxic to mosquito larvae. It has been shown that the inclusions of this bacterium contain mainly proteins of 94, 68 and 28-30 kDa. EcoRI partially digested total DNA of Btmed was cloned by using the Lambda Zap II cloning kit. Recombinant plaques were screened with a mouse polyclonal antibody raised against the 94 kDa crystal protein of Btmed. One of the positive plaques was selected, and by in vivo excision, a recombinant pBluescript SK(-) was obtained. The gene encoding the 94 kDa toxin of Btmed DNA was cloned in a 4.4 kb DNA fragment. Btmed DNA was then subcloned as a EcoRI/EcoRI fragment into the shuttle vector pBU4 producing the recombinant plasmid pBTM3 and used to transform by electroporation Bt subsp. israelensis (Bti) crystal negative strain 4Q2-81. Toxicity to mosquito larvae was estimated by using first instar laboratory reared Aedes aegypti, and Culex quinquefasciatus larvae challenged with whole crystals. Toxicity results indicate that the purified inclusions from the recombinant Bti strain were toxic to all mosquito species tested, although the toxicity was not as high as the one produced by the crystal of the Btmed wild type strain. Polyacrylamide gel electrophoresis indicate that the inclusions produced by the recombinant strain Bti (pBTM3) were mainly composed of the 94 kDa protein of Btmed, as it was determined by Western blot.