MODIFIED GENES AND THEIR EXPRESSION IN PLANT CELLS

Abstract: A DNA fragment, preferably encoding all or an insecticidally-effective part of a Bacillus thuringiensis insecticidal crystal protein, is modified by translationally neutral modifications in cryptic promoters and abortive introns.

Description: MODIFIED GENES AND THEIR EXPRESSION IN PLANT CELLS This invention provides a modified gene, such as Bacillus thuringiensis ("Bt") gene (the "modified Bt ICP gene") encoding all or an insecticidally-effective portion of a Bt insecticidal crystal protein ("ICP") . A plant, transformed wit the modified gene, shows higher expression levels of the encoded protein. Background of the Invention Plant genetic engineering technology has made significant progress during the last 10 years. It has become possible to introduce stably foreign genes into plants. This has provided exciting opportunities for modern agriculture. Derivatives of the Ti-plasmid of the plant pathogen, Aqrobacterium tumefaciens, have proven to be efficient and highly versatile vehicles for the introduction of foreign genes into plants and plant cells. In addition, a variety of free DNA delivery methods, such as electroporation, microinjection, pollen-mediated gene transfer and particle gun technology, have been developed for the same purpose. The major aim of plant transformations by genetic engineering has been crop improvement. In an initial phase, research has been focussed on the engineering into plants of useful traits such as insect-resistance. In this respect, progress in engineering insect resistance in transgenic plants has been obtained through the use of genes, encoding ICPs, from Bt strains (Vaeck et al, 1987) . A Bt strain is a spore forming gram-positive bacterium that produces a parasporal crystal which is composed of crystal proteins which are specifically toxic against insect larvae. Bt ICPs possess a specific insecticidal spectrum and display no toxicity towards other animals and humans (Gasser and Fraley, 1989) . Therefore, the Bt ICP genes are highly suited for plant engineering purposes. For more than 20 years, Bt crystal spore preparations have been used as biological insecticides. The commercial use of Bt sprays has however been limited by high production costs and the instability of crystal proteins when exposed in the field (Vaeck et al, 1987) . The heterogeneity of Bt strains has been well documented. Strains active against Lepidoptera (Dulmage et al, 1981), Diptera (Goldberg and Margalit, 1977) and Coleoptera (Krieg et al, 1983) have been described. Bt strains produce endogenous crystals upon sporulation. Upon ingestion by insect larvae, the crystals are solubilized in the alkaline environment of the insect idgut giving rise to a protoxin which is subsequently proteolytically converted into a toxic core fragment or toxin of 60-70 Kda. The toxin causes cytolysis of the epithelial midgut cells. The specificity of Bt ICPs can be determined by their interaction with high-affinity binding sites present on insects' midgut epithelia. The identification of Bt ICPs and the cloning and sequencing of Bt ICP genes has been reviewed by Hόfte and hiteley (1989) . The Bt ICP genes share a number of common properties. They generally encode insecticidal proteins of 130 kDa to 140 kDa or of about 70 kDa, which contain toxic fragments of 60 ± 10 kDa (Hόfte and Whiteley, 1989) . The Bt ICP genes have been classified into four major groups according to both their structural similarities and insecticidal spectra (Hόfte and Whiteley, 1989): Lepidoptera-specific (Cryl) , Lepidoptera- and Diptera-specific (Cryll) , Coleoptera-specific (Crylll) and Diptera-specific (CryIV) genes. The Lepidoptera-specific genes (Cryl) all encode 130-140 kDa proteins. These proteins are generally synthesized as protoxins. The toxic domain is localized in the N-terminal half of the protoxin. Deletion analysis of several Cryl genes confirm that 3' portions of the protoxins are not absolutely required for toxic activity (Schnepf et al, 1985) . Cryll genes encode 65 kDa proteins (Widner and Whiteley, 1985) . The CryllA proteins are toxic against both Lepidoptera and Diptera while the CryllB proteins are toxic only to Lepidopteran insects. The Coleoptera-specific genes (Crylll) generally encode proteins with a molecular weight of about 70 kDa (Hόfte and Whiteley, 1989) . The CrylllA gene expressed in E. coli directs th synthesis of a 72 kDa protein which is toxic for the Colorad potato beetle. This 72 kDa protein is processed to a 66 kD protein by spore-associated bacterial proteases which remov the first 57 N-terminal amino acids (Mc Pherson et al, 1988) . Deletion analysis demonstrated that this type of gene cannot be truncated at its 3 ' -end without the loss of toxic activity (Hόfte and Whiteley, 1989) . Recently an anti-coleopteran strain, which produces a 130 kDa protein, has also been described (European patent application ("EPA") 89400428.2) . The CrylV class of crystal protein genes is composed of a heterogeneous group of Diptera-specific crystal protein genes (Hόfte and Whiteley, 1989) . The feasibility of generating insect-resistant transgenic crops by using Bt ICPs has been demonstrated (Vaeck et al, 1987; Fischhoff et al, 1987 and Barton et al, 1987) . Transgenic plants offer an attractive alternative and provide an entirely new approach to insect control in agriculture which is at the same time safe, environmentally attractive and cost-effective (Meeusen and Warren, 1989) . Successful insect control has been observed under field conditions (Delannay et al, 1989; Meeusen and Warren, 1989) . In all cases, Aσrobacterium-mediated gene transfer has been used to express chimeric Bt ICP genes in plants (Vaeck et al, 1987; Barton et al, 1987; Fischhoff et al, 1987) . Bt ICP genes were placed under the control of a strong promoter capable of directing gene expression in plant cells. It is however remarkable that expression levels in plant cells were high enough only to obtain insect-killing levels of Bt ICP genes when truncated genes were used (Vaeck et al, 1987; Barton et al, 1987) . None of the transgenic plants containing a full-length Bt ICP gene produced insect-killing activity. Moreover, Barton et al. (1987) showed that tobacco calli transformed with the entire Bt ICP coding region became necrotic and died. These results indicate that the Bt ICP gene presents unusual problems that must be overcome to obtain significant levels of expression in plants . Even when using truncated Bt ICP gene for plant transformation, the steady state levels of Bt ICP itiRNA obtained in transgenic plants are very low relative to levels produced by both an adjacent NPT Il-gene, used as a marker, and by other chimeric genes (Barton et al, 1987; Vaeck et al, 1987) . Moreover, the Bt ICP full size mRNA cannot be detected by Northern blot analysis. Similar observations were made by Fischhoff et al. (1987) ; they reported that the level of Bt ICP mRNA was much lower than expected for a chimeric gene expressed from the CaMV35S promoter. In other words, the cytoplasmic accumulation of the Bt mRNA, and consequently the expression of the Bt ICP protein in plant cells, are extremely inefficient. By contrast, in microorganisms, it has been shown that truncated Bt ICP genes are less favorable than full-length genes (Adang et al, 1985) , indicating that the inefficient expression is solely related to the heterologous expression of Bt ICP genes in plants. The problem of obtaining significant Bt ICP expression levels in plant cells seems to be inherent and intrinsic to the wild-type Bt ICP genes. Furthermore, the relatively low and poor expression levels obtained in plants appears to be a common phenomenon for all Bt ICP genes. It is known that there are six steps at which gene expression can be controlled in eucaryotes (Darnell, 1982) : 1) Transcriptional control 2) RNA processing control 3) RNA transport control 4) mRNA degradation control 5) translational control 6) protein activity control For all genes, transcriptional control is considered to be of paramount importance (The Molecular Biology of the Cell, 1989) . In European patent publications ("EP") 385,962 and 359,472 efforts to modify the codon usage of Bt ICP genes to improve their expression in plant cells have been reported. However, wholesale (i.e., non-selective) changes in codon usage can introduce cryptic regulatory signals in a gene, thereby causing problems in one or more of the six steps mentioned above for gene expression, and thus inhibiting or interfering with transcription and/or translation of the modified foreign gene in plant cells. For example, changes in codon usage can cause differential rates of mRNA production, producing instability in the mRNA, so produced (e.g., by exposure of regions of the mRNA, unprotected by ribosomes, to attack and degradation by cytoplasmic enzymes) . Changes in codon usage also can inadvertantly interfere with expression of the so-modified gene. EP 359,472 suggests that plant consensus splice sites, if present in the native Bt tenebrionis coding region, be modified so as to eliminate potentially deleterious sequences. PCT patent publication WO 91/16432 describes the slow rate and/or level of nuclear production of a Bt ICP mRNA as an important cause of the relatively low expression levels of Bt ICP genes in plant cells. In particular, RNA polymerase elongation was found to be hindered in a specific region of the genes. Summary of the Invention In accordance with this invention is provided a process for modifying a gene, preferably a Bt ICP gene, particularly a cryl gene, quite particularly a crvIAb gene, whose level and/or rate of expression in a plant cell, transformed with the gene, is limited by the rate and/or level of nuclear production of a full length (i.e. unspliced) mRNA encoded by the gene; the process comprises the following step: inactivating, preferably destroying or removing, in the coding region of the gene, at least one of the following process-directing sequence elements: i) a cryptic promoter, such as a minimal promoter, in either a sense or anti-sense orientation, which can direct site-specific transcription initiation in the plant cell by partial or complete assembly of an RNA polymerase II initiation complex; particularly a cryptic promoter containing at least one DNA regulatory element such as a CCAAT sequence or a TATA sequence, or, ii) a DNA encoding an abortive intron that, at the RNA level, causes entry of a precursor mRNA species in a splicing pathway, the precursor mRNA species being processed in such a way that the resulting mRNA species does not accumulate substantially in the cytoplasm of the plant cell; the process-directing sequence elements preferably being inactivated by introducing translationally neutral modifications in the coding region of the gene by: a) introducing DNA encoding an intron, known to be efficiently spliced in the plant cell, and/or b) changing amino acid codons with others encoding the same amino acids . Also in accordance with this invention is provided a gene to be used to transform a plant cell, preferably a Bt ICP gene, particularly a cryl gene, quite particularly a crvIAb gene, that is modified by the process of this invention (a "modified gene" ) . Further in accordance with this invention, a process is provided for improving the properties, e.g. insect resistance, of a plant by transforming the plant cell genome with at least one modified gene. This invention also relates to a chimeric gene which can be used to transform plant cells and which contains the following operably-linked DNA fragments in the same transcriptional unit: 1) the coding region of the modified gene; 2) a promoter suitable for directing transcription of the modified gene in the plant cells; and 3) suitable transcript 3' end formation and polyadenylation signals for expressing the modified gene in the plant cells. This invention further relates to: a cell of a plant, the nuclear genome of which has been transformed to contain, preferably stably integrated therein, the modified gene particularly the chimeric gene; - cell cultures consisting of the plant cell; a plant which is regenerated from the transformed plant cell or is produced from the so-regenerated plant, the genome of which contains the modified gene, particularly the chimeric gene, and which shows improved properties, e.g., resistance to insect pests; seeds of the plant; and a vector for stably transforming the nuclear genome of plant cells with the modified gene, particularly the chimeric gene. Detailed Description of the Invention "Gene" as used herein means a DNA sequence encoding a protein, preferably a Bt ICP. This includes a modified or synthetic DNA sequence, as well as a naturally occurring DNA sequence, encoding a protein. "Coding region" as used herein means that part of a gene that specifies the amino acid sequence of a protein. In general, a coding region comprises a plurality of translational codons that correspond to the translated part of the fully processed mRNA. "Bt ICP gene" as used herein means a DNA sequence encoding a Bt ICP which is derived directly or indirectly from B. thurinσiensis. This includes a modified, a synthetic or a naturally occurring DNA sequence, encoding a Bt ICP. As used herein, "truncated Bt gene" should be understood as a fragment of a full-length Bt gene which still encodes at least the toxic part of the Bt ICP, preferentially the toxin. As used herein, "Bt ICP" should be understood as an intact protein which can be produced in nature by B. thuringiensis or a part or derivative of such a protein which has insecticidal activity. A Bt ICP can be a protoxin, as well as an active toxin or other insecticidal truncated part of a protoxin which need not be crystalline and which need not be a naturally occurring protein. An example of a Bt ICP is a Bt2 insecticidal crystal protein (Hόfte et al, 1986; the terminology of Bt2 is according to Hόfte and Whiteley (1989) "CrylAb"), as well as its insecticidally effective parts which are truncated at its C- and/or N-terminal ends towards its trypsin cleavage site(s) and preferably having a molecular weight of 60-80 kDa. Other examples of Bt ICPs are: lepidopteran-active ICPs like Bt3, Bt4, Btl4, Btl5, Btl8, Bt73, crylG described in Gleave et al (1992), crylF described in EP 405,810; and coleopteran-active ICPs like: Btl3, Bt21, Bt22, BtI260 and BtI109P as disclosed in PCT publications WO 90/15139 and WO 90/09445, in Hόfte and Whiteley (1989) and in EPA 90403724.9, or any modified or hybrid ICPs having insecticidal activity. As used herein, "protoxin" should be understood as the primary translation product of a full-length gene encoding a Bt ICP. As used herein, "toxin" or "active toxin" or "toxic core" should all be understood as a part of a protoxin which has insecticidal activity and which can for instance be obtained by protease (e.g. by trypsin) cleavage. As used herein, a "process-directing sequence element" is a genetically cis-acting regulatory element that is either a DNA encoding an abortive intron or is a cryptic promoter whose presence in the coding region of a gene in a plant cell substantially inhibits or prevents the gene's transcription to a full length mRNA, the nuclear accumulation of a full length mRNA and/or the nuclear export of a full length mRNA. Such a sequence element can be different from known plant promoters or plant introns in a given plant cell. A process-directing sequence element would, if not inactivated, actually be recognized by a plant cell and thereby would interfere with gene expression in the plant cell. A genetically cis-acting regulatory element of this invention is believed to be involved in, and/or responsible for, a gene expression-controlling step, such as is listed in the Background of the Invention, that interferes with gene, particularly Bt ICP gene, expression in plant cells. A "cryptic promoter", such as a "minimal promoter", as used herein means a DNA sequence which is located within the coding region of a protein-encoding gene in either a sense or anti-sense orientation and which can direct site-specific transcription initiation in a given plant cell by partial or complete assembly of an RNA polymerase II initiation complex. Such cryptic promoters are believed to be active due to th presence of so-called "DNA regulatory elements" which are cis acting, such as the CCAAT and TATA sequences, whic specifically interact with nuclear factors. It appears that cryptic promoter interferes with gene expression by interactin with nuclear proteins and thereby causing transcriptional interference to RNA polymerase II transcribing the gene, or by being transcriptionally active and thereby specifying, depending on its orientation within the gene, a sense or anti- sense RNA, causing sense or anti-sense suppression of gene expression. A "DNA regulatory element" herein is a sequence in a promoter region that is involved in the partial or complete assembly of an RNA polymerase II initiation complex. Known examples of such DNA regulatory elements are the TATA box and the CCAAT box (Ha and An, 1989; Paul et al, 1987), which in many plant promoters are separated by about 20 to 50 nucleotides, with the TATA box being located about 32 ± 7 nucleotides upstream from the transcription initiation site (Joshi, 1987) . Other known DNA regulatory elements are, for example, those listed by Katagiri and Chua (1992) . A "precursor mRNA" or "pre- RNA" refers to the protein- encoding RNA that is transcribed from the DNA in the nucleus of a plant cell. A pre-mRNA can be further processed, for instance by the removal of plant introns, and the fully-processed or mature mRNA is ultimately translated in the cytoplasm of the plant cell. As used herein a "full length mRNA", a "fully processed mRNA", or a "mature mRNA" is an mRNA that can be translated in the cytoplasm and encodes the protein encoded by the gene. "Abortive splicing" as used herein is a process in which a precursor mRNA species enters a splicing pathway of a plant cell and is processed in such a way that the spliced mRNA does not accumulate substantially in the plant cell cytoplasm, e.g. the mRNA decays during or after splicing in the nucleus before transport to the cytoplasm or it decays rapidly in the cytoplasm. It appears that in abortive splicing, only a relatively small number of the pre-mRNAs are effectively processed with removal of an intron and subsequent junction of the exon, whereby only the actually spliced mRNAs are detectable in some or all plant cells. Abortive splicing should not be confused with partially active splicing in which a majority of the pre-mRNAs which enter the splicing pathway are effectively spliced, but with only a low frequency of such pre- mRNAs actually entering the splicing pathway. An "abortive intron" is any RNA sequence which is present in a pre-mRNA and which is removed when the pre-mRNA is abortively spliced in a plant cell. A gene may encode more than one abortive intron, and it is believed that abortive splicing thereof is part of an ordered process with dominant intron (s) being spliced out first and with less dominant introns being spliced out later in a plant cell. "Abortive intron splice sites" as used herein are those nicking sites at the 5' and 3' sides of an abortive intron at which splicing occurs in any pre-mRNA that is abortively spliced. In accordance with this invention, a cryptic promoter in the coding region of a particular gene, preferably a Bt ICP gene, can be detected by the following procedure: In a first step a region (the "pausing region") is identified in the gene where transcription elongation is substantially inhibited. Pausing is the process by which the elongation rate of RNA polymerase II, active in transcription, reduces. Pausing differs from termination in that RNA polymerase II remains associated to the template and can resume RNA synthesis. A pausing region in a transcription unit can be determined by measuring the transcriptional activity of RNA polymerase II complexes transcribing the gene, for example by run-on analysis as described in PCT patent publication WO 91/16432, for consecutive, partially overlapping regions of the gene of about 300 nucleotides, preferably of about 200 nucleotides, particularly of about 100 nucleotides. A pausing region corresponds to such region in which the transcriptional activity is low, preferably less than 20%, particularly less than 10%, quite particularly less than 5% relative to the activity in a region of about 300 nucleotides directly downstream of the transcription initiation site, particularly when the run-on assay is performed for a prolonged time period, i.e. for a period of 5 to 10 minutes. Nuclei to be used in the run-on assay can be obtained by nuclei purification methods using either transiently or stably transformed cells carrying the gene respectively extra- or intra-chromosomally. If transgenic plants are available in which the nuclear genome is transformed with the gene under control of appropriate plant gene regulatory sequences, the pausing region can be determined by nuclear run-on assays, supplemented by DMS footprinting analysis, as for instance described in the examples, and/or the KMn0 4 pausing assay (Morrett and Buck, 1989; Sasse-Dwight and Gralla, 1988; Cannon et al, 1990) . Once the pausing region has been determined parts or all of it (generally regions of about 100 to 300 nt in length) can be cloned into two orientations in a suitable transcription initiation-probe vector (Cornelissen and Vandewiele, 1989a) . Such a vector can, for example, be obtained by placing part or all of the pausing region downstream of an enhancer of a plant promoter and upstream of a DNA sequence that can be transcribed and the transcript of which can be uniquely detected in plant . cells. A preferred example of such an enhancer is the enhancer or "B" region of the 35S promoter as described by Benfey et al (1990) , but other known enhancer regions can also be used (as for instance the enhancer of the TR2' promoter) . Preferred examples of a transcribable region in the transcription initiation probe-vector are the coding regions of the bacterial chloramphenicol acetyl transferase gene (cat) or the basta-resistance gene (Cornelissen and Vandewiele, 1989a) , followed by a suitable 3' end formation and polyadenylation sequence. When these vectors are introduced into plant cells such as tobacco or maize protoplasts, one can then detect the accumulation of particular transcript species which are initiated from the presumed cryptic promoter by hybridization with a probe derived from the transcribable region of the transcription initiation probe-vector. Primer extension analysis or SI mapping of the transcripts then allows the determination of the transcription initiation site which in turn facilitates the detection of potential DNA regulatory elements, such as CCAAT and TATA boxes that are recognized by the plant cell. If known DNA regulatory elements in a suitable configuration to be recognized by the plant cell (e.g. a CCAAT box and a TATA box separated by about 20 to 50 nucleotides) are found in the sequence this is already a strong indication of the presence of a cryptic promoter and this can be confirmed by assaying for the ability to initiate transcription by placing the region containing these elements in the transcription initiation- probe vector as described above. Typically the start site of transcription is maintained when the enhancer is moved relative to the cryptic promoter over distances shorter than 50 nucleotides, preferably 100 nucleotides, more preferably 200 nucleotides . In accordance with this invention, an abortive intron in the coding region of a particular gene, preferably a Bt ICP gene, can be detected by the following procedure: The coding region of the gene is placed under control of suitable plant regulatory sequences in a suitable vector and introduced in plant cells, such as tobacco or maize protoplasts. About 5 to 7 hours after DNA delivery, total RNA is extracted. cDNA is prepared from the mRNA that is present in the plant cells according to conventional methods. Subsequently overlapping regions of the full size precursor mRNA expected to be produced from the introduced gene are amplified by means of PCR, using the previously synthesized cDNA as a substrate and using gene specific oligonucleotide primer pairs that lie between the transcript start site and the 3' end formation site. In general overlapping regions of about 500 to 700 nucleotides are amplified, but this can be supplemented with amplification of increasingly larger overlapping regions e.g. amplification of overlapping regions of about 1000 nucleotides possibly followed by amplification of overlapping regions of about 2000 nucleotides will be generally suitable for this purpose. The amplified products are then analyzed and any product that is smaller in size than that expected on the basis of full-size, mature mRNA is purified and sequenced. A comparison of the sequence of such shorter amplified products with the sequence of the expected full size precursor mRNA then allows the identification of gaps in the amplified products corresponding to introns. This in turn allows the identification of presumed intron splice sites at the 5 ' and 3' ends of the introns in the expected full-size mRNA. Inactivation of the 5' splice site and reintroduction of the gene into plant cells will allow to distinguishbetween abortive andpartially active introns. If the intron is abortive, inactivation of the splice site will result in significant increases in full size mRNA levels, whereas inactivation of the partially active intron will result in a marginal increase of the full length mRNA level. The routine system used for the identification of cryptic promoters or abortive introns as described above is the transient expression (TEX) protoplast system. For dicots, tobacco cells are preferred for the identification of the active process-directing sequence elements; for monocots, corn or rice cells provide the preferred test system. Of course, any plant cell, known in the art as suited for transient or stable transformation, can be used. The identification and characterization of cryptic promoters and/or abortive introns of this invention allows the recognition of relatively small DNA sequence elements (the "target sequences") and their modification so as destroy the activity of these process- directing sequence elements in the plant cell. It is preferred that such modifications be translationally neutral. "Translationally neutral modifications" as used herein are modifications that do not affect the amino acid sequence of the protein encoded by the gene. Preferred examples of such translationally neutral modifications are the changing, by means of nucleotide substitutions in the gene, of amino acid codons into others codons that encode the same amino acids. Such nucleotide substitutions can change A and T nucleotides into C and G nucleotides (PCT patent publication WO 91/16432) , and for certain other translationally neutral modifications, C and G nucleotides may be changed to A and T nucleotides. Another preferred example of translationally neutral modifications is the introduction in the gene of at least one intron, known to be efficiently spliced in plant cells, so that the gene is transcribed into a precursor mRNA that is efficiently processed, by means of splicing of the introduced intron, into a mature mRNA that codes for the protein, preferably the Bt ICP. An intron known to be efficiently spliced in plant cells is any intron that is efficiently spliced out of a precursor mRNA in the plant cell. A suitable intron for use in plants, preferably in dicots, is the TA36 intron, as described in PCT patent publication WO 92/13957 or any other functional plant intron. Appropriate sites for insertion of the TA 36 intron or any other functional plant intron are determined according to well known general rules as outlined, for example, in Goodall and Filipowicz (1989) and Hanley and Schuier (1988) . Of course, translationally neutral nucleotide substitutions can be combined with the introduction of such introns in a foreign gene to be expressed in a plant. The DNA regulatory elements, such as the CCAAT and/or TATA boxes, present in a cryptic promoter are preferred target sequences for modification. Thus the sequence of such DNA regulatory elements can be changed by translationally neutral nucleotide substitutions of selected nucleotides and/or by insertion in that sequence of a suitable plant intron. However, plant cell recognition of the cryptic promoter can be reduced or eliminated by making substantial translationally neutral changes throughout the zone of 20 to 90, preferably 20 to 50, nucleotides upstream of the experimentally determined transcription initiation site. Preferably, such substantial changes will comprise making the maximum possible number of translationally neutral nucleotide substitutions within this zone. Also, the introduction of a suitable plant intron at any appropriate position in this zone is believed to reduce the activity of the cryptic promoter. With respect to the abortive introns, it is believed that the abortive intron splice sites are of particular importance for the entry of the precursor mRNA containing the abortive intron in the abortive splicing pathway. Abortive introns are preferably inactivatedby translationally neutral modifications in the coding region of the gene, preferably the Bt ICP gene, in the sequence corresponding to that surrounding at least the 5' (or upstream) abortive splice site in the precursor mRNA transcribed from the gene in a plant cell. Of course these modifications may be supplemented with, or even replaced by, modifications in the sequence of the coding region corresponding to that surrounding the 3' (or downstream) abortive splice site and/or the branch point (Brown, 1986) . Preferred target sequences are thus believed to be a sequence of about 10 nucleotides, particularly a sequence of about 5 nucleotides, quite particularly a sequence of about 3 nucleotides, on either side of the sites that, in the precurso mRNA transcribed from the gene, correspond to the 5' and/or 3' abortive splice sites of the abortive intron, preferably its 5' GT and/or its 3' AG nucleotides. Abortive introns according to this invention have certain essential characteristics of plant introns as described for example by Goodall and Filipowicz (1989, 1990) . Furthermore, examples of target sequences for abortive intron modification can be found in the consensus RNA sequences essential for intron splicing (Padgett et al, 1986; Aebi and Weismann, 1988) in plant cells as described by Hanley and Schuier (1988) as follows (' refers to the splice position) : N A/U G ' G U A A G U/A A/U U/A U/A at the 5' border of introns of dicots and U/A U/A U/N U/A U/A U/A U/A A/U U/A U/A U G/A C/U A G ' at the 3' border of introns of dicots; and A/C/G A G ' G U A A/U G U/C U/A U/C U/N at the 5' border of introns of monocots and U/C U/C U/G U/A U/C U/G U/N U/N U G/N C A G ' at the 3' border of introns of monocots. Surprisingly, many non-plant genes, particularly Bt ICP genes, have been found to encode the following portions of the consensus RNA sequences of Hanley and Schuier (1988) that are essential for intron splicing in plant cells: GUAAG or GUAUG, particularly GUAAG, downstream (i.e., 3') of the upstream (i.e., 5') intron splice position; and AG upstream of the downstream intron splice position. Thus the modification of a cryptic promoter and/or of the DNA encoding an abortive intron, preferably in specific target sequences, particularly by removing the essential characteristics or destroying the DNA encoding the consensus RNA sequences, as described above, results in an increased amount of full-size mRNA that can be translated to produce the protein encoded by the gene. As used herein, "modified gene" should be understood as a DNA sequence, preferably one that encodes a Bt ICP, and in which, in at least one process-directing sequence element of the coding region, the nucleotide content of at least one codon has been changed by a translationally neutral modification that results in the inactivation of such a process-directing sequence element. Preferably, only minor modifications are made to the coding region of the Bt ICP gene. In particular, the modifications involve changing less than 10%, preferably less than 3%, particularly less than 1%, of the nucleotides in the coding region. In this regard, less than 10%, preferably less than 3%, particularly less than 1%, of the nucleotides in the coding region of the gene are changed from A or T nucleotides to G or C nucleotides. However, modifications of the coding region in accordance with this invention do not require the introduction of plant preferred codons, nor do they require that only A and T nucleotides are changed to G and C nucleotides. Preferably, each of the process-directing sequence elements is modified by changing only few nucleotides, so that the element is inactivated in the given plant cell, and so that the nucleotides encode the same amino acids. However, in some instances, some amino acids can be changed, such as when an encoded Bt ICP retains at least substantially the same insecticidal properties. This invention is preferentially applied to genes which are to be expressed into certain plant species but that originate from organisms that are only distantly related to those plant species, e.g., expressing bacterial or animal genes in plants, monocot genes in dicots or dicot genes in monocots. In this regard the invention is particularly useful for modifying genes which are A+T-rich, particularly genes which contain more than 50% A+T in certain regions, such as Bt ICP genes, especially the cryl genes, more specifically the crvIAb gene. The present invention will be exemplified by means of the crvIAb or bt2 gene of Bacillus thuringiensis. Thus it has been shown previously that the expression pathway of a Bt ICP gene, such as bt2, bt!4, bt!5 and bt!8, is specifically inhibited at the nuclear level in plant cells (PCT patent publication WO 91/16432 which is incorporated herein as reference) . Nuclear run-on analysis with N28 - 220 nuclei, originating from tobacc cells and containing the bt884 construct (Vaeck et al . , 1987) , indicated that transcription elongation of the nascent Bt ICP mRNA was impaired between or close to nucleotides 700 to 1000 downstream of the start of transcription. Filter binding assays using labeled Bt DNA fragments spanning this region and protein extract prepared from tobacco nuclei revealed that this DNA region undergoes specific interactions with proteins present in nuclei (PCT publication WO 91/16432) . In vivo transcription initiation assays (Cornelissen and Vandewiele, 1989a) in which the 474 bp EcoRV-Bstll07i bt884 fragment is positioned downstream of the CAMV 35S enhancer, have now revealed that this region functions as a minimal promoter in tobacco and as such can interact with nuclear transcription factors. These interactions are the prime candidates that cause or affect the impaired elongation of transcription by RNA polymerase II through this region. By modification of this region to abolish specific protein binding, Bt ICP expression levels will increase. This region has been found to contain CCAAT- and TATA- sequences, which are conserved motifs, found in promoters of diverse origin (The Molecular Biology of the Cell, 1989) . Deletion analysis suggested that the low transcript levels produced by Bt ICP genes were not controlled by a single factor (PCT publication WO 91/16432) . A study of the polyadenylated bt884 transcripts in N28-220 by cDNA-PCR revealed the occurrence of minor quantities of shorter transcript species. Sequence analysis of the PCR products demonstrated the presence of three cryptic introns in the bt884 coding region. It can not be excluded that additional or other splicing events, including abortive splicing, take place when the bt884 is expressed in other plant species. In accordance with the deletion analysis, this finding demonstrates that a plurality of inhibitory zones are present in the bt884 coding region. Nevertheless, individual modifications of the bt884 o crvIAbδ coding region can significantly reduce the interferenc and/or inhibition of the expression of the full length mRN encoded by the genes in plant cells at the level of transcrip elongation, nuclear processing, nuclear accumulation an nuclear export. The modification(s) may also affect cytoplasmi regulation and metabolism of such mRNAs and their translation. In addition, substitution mutations were made at the 5' splice sites of each of the three cryptic introns. These mutations are translationally neutral, and as such abolish splicing of the respective introns. bt884 or cr IAb6 genes carrying these modifications direct significantly higher levels of full length mRNA and ICP in tobacco cells compared to the wild-type gene. Instead of modifying the codon usage of one or more inhibitory zones in a Bt ICP gene, such as bt884 or cryIAb6, at least one process-directing sequence element in each such zone, preferably each of such sequence elements in each inhibitory zone, is inactivated, preferably split by providing at least one intron within it. The intron preferably provided in the inhibitory sequence is efficiently spliced in the plant cell, and is not intended to provide a so-called "intron-mediated elevation of gene expression" as has been reported for several genes that were transiently introduced in corn cells (Callis et al, 1987) . Instead, the intron is intended to destroy the functioning of the inhibitory sequences by dividing the sequence in two. This modification leaves the coding region of the Bt ICP gene otherwise unaffected, while changing its regulatory features in regard to processes preceding the accumulation of mature mRNA in the nucleus and/or cytoplasm. However, to optimize the splicing efficiency of precursor mRNAs, it may be necessary to modify the nucleotides flanking the introduced intron, preferably with at most three nucleotides, spread over at most two translational codons, to create optimal 5' and 3' splice boundaries. According to Brown (1986) , 38 out of 64 possible nucleotide triplets can each serve as a 5' exon boundary flanking an intron in an endogenous plant gene in a plant, and any nucleotide can be used at the 3' exon boundary flanking such an intron. Triplets not described by Brown (1986) can also function as such 5' exon boundaries in a plant. By way of example the 5' splice site of intron 2 was interrupted in the crylAbδ coding region by introducing the intron sequence of the tobacco gene TA36. This modified gene directs elevated levels of full length crylAbδ mRNA in tobacco cells. In the modified Bt ICP gene all process-directing sequence elements, active in the plant cell, can be removed or destroyed, or only some can be removed or destroyed, depending on the expression level desired. Preferably, the modified gene, such as the modified Bt ICP gene, is inserted in a plant genome downstream of, and under the control of, a promoter which can direct the expression of the gene in the plant cells. Preferred promoters include, but are not limited to, the strong constitutive 35S promoter (Odell et al, 1985) or duplicated 35S promoter (Kay et al, 1987) of cauliflower mosaic virus; 35S promoters have been obtained from different isolates (Hull and Howell, 1987) . Other preferred promoters include the TR1' promoter and the TR2 ' promoter (Velten et al, 1984) . Alternatively, a promoter can be utilized which is not constitutive but rather is specific for one or more tissues or organs. For example, the modified gene can be selectively expressed in the green tissues of a plant by placing the gene under the control of a light-inducible promoter such as the promoter of the ribulose - 1,5 biphosphate - carboxylase small subunit gene as described in EPA 86300291.1. Another alternative is to use a promoter whose expression is inducible by temperature or chemical factors. It is preferred that the coding region of the modified gene, such as the modified Bt ICP gene, be inserted upstream of suitable 3' transcription regulation signals (i.e., transcript 3' end formation and polyadenylation signals) derived from the chalcone synthase gene (Sommer and Saedler, 1986) or Cauliflower Mosaic Virus (Mogen et al, 1990) , the octopine synthase gene (Gielen et al, 1984) , or T-DNA gene 7 (Velten and Schell, 1985) . In accordance with this invention, all or part of a modified gene of this invention, such as a modified Bt ICP gene, can be stably inserted in a conventional manner into the nuclear genome of a plant cell, and the so-transformed plant cell can be used to produce a transgenic plant showing improved expression of the modified gene. In this regard, a disarmed Ti-plasmid, containing the modified gene, in Agrobacterium (e.g., A. tumefaciens) can be used to transform a plant cell using the procedures described, for example, in EP 116,718 and EP 270,822, PCT publication 84/02913, EPA 87400544.0 and Gould et al (1991) (which are incorporated herein by reference) . Preferred Ti-plasmid vectors contain the foreign DNA sequence between the border sequence, or at least located to the left of the right border sequence, of the T-DNA of the Ti-plasmid. Of course, other types of vectors can be used to transform the plant cell, using procedures such as direct gene transfer (as described, for example, in EP 233,247), pollen mediated transformation (as described, for example, in EP 270,356 PCT publication WO85/01856, and US patent 4,684,611), plant RNA virus-mediated transformation (as described, for example, in EP 67,553 and US patent 4,407,956), liposome-mediated transformation (as described, for example, in US patent 4,536,475) and other methods such as the methods for transforming monocots such as the major cereals including corn, rice, wheat, barley and rye, as described in PCT patent publication WO 92/09696. In case the plant to be transformed is corn, other recently developed methods can also be used such as, for example, the method described for certain lines of corn by Fromm et al (1990), Gordon-Kamm et al (1990), and Gould et al (1991) . In case the plant to be transformed is rice, recently developed methods can also be used such as, for example, the method described for certain lines of rice by Shimamoto et al (1989), Datta et al (1990) and Hayashi oto et al (1990) . The resulting transformed plant of this invention shows improved expression of the modified gene, such as the modified Bt ICP gene, and hence is characterized by the production of high levels of protein, such as Bt ICP, encoded by the gene. Such a plant can be used in a conventional breeding scheme to produce more transformed plants with the same improved properties such as insect-resistance characteristics or to introduce the modified gene like the modified Bt ICP gene into other varieties of the same or related plant species. Seeds, which are obtained from the transformed plants, contain the modified gene as a stable geno ic insert. It is believed that expression of a foreign gene in a plant can be improved in accordance with this invention for any plant such as corn, soybean, oilseed rape, wheat, lettuce, tomato and potato. However, the modification of genes intended to be expressed in monocots may require the translationally neutral modification of process-directing sequence elements having different DNA or RNA sequences from those active in dicots. Furthermore, at least two modified Bt ICP genes, coding for two non-competitively binding Bt ICPs, can be cloned into a plant expression vector (EPA 89401499.2) . Plants transformed with such a vector are characterized by the simultaneous expression of at least two modified Bt ICP genes. The resulting transgenic plant is particularly useful to prevent or delay development of resistance to Bt ICP of insects feeding on the plant . This invention is thus based on the discovery that the coding region of foreign genes, particularly bacterial genes, quite particularly Bt ICP genes, may contain genetically cis- acting regulatory elements in their coding regions, particularly cryptic promoters and abortive introns, that seriously hamper the expression of these genes when they are introduced, under control of appropriate plant regulatory sequences such as plant promoters and 3' untranslated ends, in a plant cell environment. The discovery of such sequences allows the directed and limited modification of target sequences within the coding regions of such genes. In general less than about 10%, preferably less than about 3%, nucleotide modifications in the coding region are required in order to substantially alleviate the expression problem. Because only a relatively small number of modifications result in a substantial increase of foreign gene expression in plants, the modified genes produced in accordance with this invention are unlikely to contain newly introduced sequences that interfere themselves with expression of the gene in a plant cell environment. The following Examples illustrate the invention and are not intended to limit its scope. The Figures and Sequence Listings, referred to in the Examples, are as follows: Figures: Fig. 1 - Comparison of the transcriptional activity of neo and bt884 genes in nuclei of N28-220 of Example 1. The RNA extension reaction was performed in the presence of J ~P UTP for 20 minutes at 30°C. Radioactively labeled RNA extracted from nuclei was hybridized with a molar excess of denatured neo and bt884 DNA which was immobilized on a nylon membrane. The positions and sizes of the DNA regions on the T-DNA are indicated. LB and RB refer to the left and right T-DNA borders, respectively. The 3'end formation and polyadenylation region of the gT. aπ -d ocs genes (Vaeck et al, 1987) are indicated. The relative abundance of hybridizing neo (left-hand column) and bt884 (right-hand column) mRNAs was measured both by scintillation counting and densitometric scanning of autoradiographs with different exposure times. Values were corrected for the UTP contents of the hybridizing RNA. Fig. 2 - Schematic representation of the DMS footprint of th bt884 coding region between nucleotides 668 and 834. Nucleotides hyper- and hypo-methylated in vivo relative t naked DNA by DMS are indicated by arrows pointing respectivel downwards and upwards. See the scales at the right of th figure for quantification. All maintenance greater than 15% an hypersensitivities greater than 1.25 fold are shown. Boxe G-residues were not taken into account as the correspondin bands comigrated with dimers of the radioactively labele primers. The CCAAT boxes are underlined. Fig. 3a - Schematic view of the bt884 coding region with four PCR primer sets of Example 4. Nucleotide numbering is relative to the translation start codon. The orientations of the PCR primers are indicated by arrows, and the position of the 5' nucleotide of each primer is shown. Fig. 3b - Schematic views of three DNA fragments (I, II and III) obtained by PCR reactions with primers PS58 and PS59. Numbering is relative to the translation start codon and refers to the 5' and 3' nucleotides of the introns in the bt884 coding region. The adjacent nucleotides located upstream and downstream of the 3' and 5' splice sites are shown. Sequence Listing: SEQ ID NO. 1: oligonucieotide PS48 SEQ ID NO. 2: oligonucieotide PS43 SEQ ID NO. 3: oligonucieotide PS38 SEQ ID NO. 4: oligonucieotide PS39 SEQ ID NO. 5: oligonucieotide PS47 SEQ ID NO. 6: oligonucieotide PS44 SEQ ID NO. 7: oligonucieotide PS38 SEQ ID NO. 8: oligonucieotide PS46 SEQ ID NO. 9: oligonucieotide PS45 SEQ ID NO. 10: oligonucieotide PS58 SEQ ID NO. 11: oligonucieotide PS59 SEQ ID NO. 12: oligonucieotide PS61 SEQ ID NO. 13: oligonucieotide PS62 SEQ ID NO. 14: oligonucieotide PS63 SEQ ID NO. 15: oligonucieotide PS64 SEQ ID NO. 16: oligonucieotide PS65 SEQ ID NO. 17: oligonucieotide PS66 SEQ ID NO. 18: oligonucieotide RVA-5a SEQ ID NO. 19: oligonucieotide RVA-5b SEQ ID NO. 20: oligonucieotide RVA-6a SEQ ID NO. 21: oligonucieotide RVA-6b SEQ ID NO. 22: plasmid pJD884 SEQ ID NO. 23: plasmid pPS0212 Unless otherwise stated in the Examples, all procedures for making and manipulating recombinant DNA are carried out by the standardized procedures described in Sambrook et al, Molecular Cloning - A laboratory Manual, Cold Spring Harbor Laboratory Press, NY (1989) . Particular nucleotides in the bt884 and crvIAb6 genes, as used in the examples, are identified with respect to the sequence of the genes as given in SEQ ID NO. 22 and SEQ ID NO. 23 respectively. Plasmid pJD884, the complete sequence of which is given in SEQ ID NO. 22, contains the bt884 gene and was used to construct plasmids pRVA0214 and pPS0212. In this regard pRVA0214 is identical to pJD884 except that the sequence containing the ATG translation initiation codon between nucleotide positions 7630 and 105 is replaced with the corresponding sequence between positions 7546 and 6 of SEQ ID NO. 23; this results in a deletion of 28 amino acids at the N-terminus of the bt884 gene, and the introduction of a Joshi translation initiation consensus sequence (The corresponding bt2-derived gene in PRVA0214 is designated as crvIAb22) . Plasmid pPS0212, the complete sequence of which is given in SEQ ID NO. 23, differs from pRVA0214 by several translational neutral nucleotide substitutions in the regions located between nucleotides 1 to 30 and between 594 to 906. Example 1. Cryptic promoter activity Nuclear run-on data obtained with transgenic tobacco N28- 220, described in PCT patent publication WO 91/16432, indicated that the low nucleo-cytoplasmic full length bt884 mRNA flow is not due to interference of the bj; coding region with transcription initiation at the TR2 ' promoter (Fig.l) and that elongation by RNA polymerase II was inhibited between or close to nucleotides 700 and 1000 downstream of the transcriptional start site of the bt884 gene. Furthermore, DNA footprint analysis showed that in vivo DNA binding proteins interact with the bt884 DNA region between nucleotides 670 and 1202 (nucleotide positions are measured relatively to the translation initiation codon) . The result of this interaction could be that RNA polymerase II complexes encounter difficulties in elongating transcripts in this region. Inspection of the region revealed the presence of a number of CCAAT boxes . An in vitro dimethyl sulfate (DMS) footprint was carried out of the region 667 to 835, downstream of the translation start of bt884, to identify if in vivo the CCAAT boxes undergo a DNA-protein interaction. Protoplasts of N28-220 were treated for 3 minutes with 0.5% DMS, and total DNA was prepared (Dellaporta et al, 1983) . A parallel reaction was carried out at pH 7.9 with 34 μg of deproteinized DNA of N28-220 in 200 μl TE (10 mM Tris, pH 7.9, ImM EDTA) to which lμl DMS was added. The incubation was stopped after three minutes by the addition of 100 μl 3M Tris, pH 8.0, followed by a phenol-chloroform extraction. The DNA samples were nicked 5' to the methylated G residues by a piperidine incubation (Maxam and Gilbert, 1980) . DNA strands nicked near the bt2 (crvIAb) pausing region were amplified according to the ligation-mediated PCR method described by Mueller and Wold (1989) using 3.5 μg DNA samples for both reactions. The oligonucleotides used in the first priming reaction were: the oligonucieotide of SEQ ID NO. 1 for the coding strand and oligonucieotide of SEQ ID NO. 2 for the non-coding strand. The following linkers were ligated: th oligonucieotide of SEQ ID NO. 3 and the olignucleotide of SE ID NO. 4. The ligation product was amplified by 19 PCR cycles, using for the coding and non-coding strands the respective oligonucleotides: the oligonucieotide of SEQ ID NO. 5 and the oligonucieotide of SEQ ID NO. 6, together with the linker of SEQ ID NO. 7. A last amplification reaction of the coding and non-coding strands was done with respectively: the oligonucieotide of SEQ ID NO. 8 and the oligonucieotide of SEQ ID NO. 9 which were end-labeled with i; P. The reaction products were separated on a sequencing gel and visualized by autoradiography. The lanes were scanned three times with a LKB Ultrascan 2002 (Pharmacia LKB Biotechnology, Uppsala, Sweden) and compared by alignment of the recorded profiles. The nucleotide positions were plotted versus the ratio of the densitometric values of the G-residues at the different positions in the in vivo and in vitro DMS footprints. A linear regression was determined by reiterated calculation using points that deviated less than 20% from the average slope. Hyper- and hypo-methylation levels were determined by calculating the relative deviation of the in vivo signals for the calculated relation. The result of the DMS footprint is shown in Fig. 2. The two closely spaced CCAAT boxes, and not a separately located CCAAT box more upstream, clearly show a modulated sensitivity to DMS in vivo relative to in vitro. This strongly suggests that these boxes undergo in vivo a protein-DNA interaction. As the bt. coding region has a high AT content, the CCAAT boxes might be in the proximity of a functional TATA box and thus be part of a minimal promoter. To test this hypothesis, the 474 nucleotide EcoRV-Bstll07l bt884 fragment was positioned in a sense orientation between the CaMV 35S enhancer fragment and a promoterless cat gene to monitor possible transcription initiation events (Cornelissen and Vandewiele, 1989a) . When introduced into tobacco protoplasts, the 35S enhancer CCAAT box fusion directs the synthesis of two discrete cat mRNA species. An Sl-protection assay was carried out essentially as described by Sambrook et al (1989) to determine the 5' nucleotides of the cat mRNAs. This resulted in the identification of three different 5' termini. The 5' termini are present in approximately equimolar ratios and map at nucleotides 774, 775, 777; nucleotides 833, 834, 836; and nucleotide 841, relative to the translation start site of bt884. This finding shows that this region functions as a minimal promoter element and as such can interact with transcription factors. The consequence of this interaction is believed to result in the incapacity of RNA polymerase II to of transcribe efficiently this region. Example 2. Detection of bt884 mRNA processing PCT patent publication WO 91/16432 shows that the low cytoplasmic bt884 mRNA levels in tobacco are due to a limited flow rate of full length bt884 mRNA to the cytoplasm. The run- on analysis in combination with the deletion analysis described in PCT publication WO 91/16432 show that crylAb transcript elongation in N28-220 is hindered between or close to nucleotides 700 and 1000, downstream of the start site of transcription initiation and that either several regions of the cr IAb coding region are involved in this process or transcriptional pausing at a cryptic promoter is not the sole process which interferes with expression. To determine whether other processes are interfering with cytoplasmic bt884 mRNA accumulation, the integrity of the polyadenylated bt884 transcripts expressed by N28-220 was analyzed. The bt884 mRNA accumulates at levels which are below the detection limit of conventional Northern blot analyses of total RNA (Vaeck et al, 1987) . The bt884 mRNA expressed by N28-220 was therefore studied as follows. Mesophyll protoplasts of N28-220 were prepared as described by Denecke et al (1989) . Total RNA was extracted according to Jones et al (1985), and a cDNA reaction was carried out using, as a DNA primer, oligo(dT) essentially as described by Kawasaki (1990) . The first strand was used to amplify a specific DNA fragment employing the Polymerase Chain Reaction (PCR) as described by Kawasaki (1990) using the following sets of primers: set A: PS66 and PS64, set B: PS63 and PS65, set C: PS58 and PS59, set D: PS61 and PS62, the primers being shown in the sequence listing as follows: PS58 in SEQ ID NO. 10, PS59 in SEQ ID NO. 11, PS61 in SEQ ID NO. 12, PS62 in SEQ ID NO. 13, PS63 in SEQ ID NO. 14, PS64 in SEQ ID NO. 15, PS65 in SEQ ID NO. 16, and PS66 in SEQ ID NO. 17. The amplified DNA products were run on a nondenaturing polyacrylamide gel, and primer sets A and B yielded DNA fragments of the expected size (Fig. 3a) . Primer set C yielded, in addition to the expected DNA fragments, two additional DNA species of smaller size (II and III in Fig. 3b) . Sequence analysis (Maxam and Gilbert, 1980) of the DNA fragments generated by primer set C revealed the presence of one and two deletions in the amplified bt884 DNA sequences II and III, respectively. The nucleotide sequences of the extremities of the deleted portions are in agreement with the sequences of consensus sites of plant intron borders of Hanley and Schuier (1988) i.e., GT at the 5' end of each deleted portion and AG at the 3' end of each deleted portion (Fig. 3b) . The size of the deletions was respectively 208 and 139 nucleotides. Primer set D yielded in addition to the expected DNA product, four smaller PCR products. Sequence analysis of these fragments confirmed the occurrence of the 208 nucleotides deletion and the combination of the 208 and 139 nucleotides deletion as was seen with the cDNA-PCR analysis using primer set C, as well as the combination of the 208 nucleotides and a novel 929 nucleotides deletion. The extremities of this latter deleted sequence agree with the consensus sites of 5' and 3' RNA splice sites. The deletions thus reveal that the bt884 precursor mRNA undergoes splicing, the exact location of two of its cryptic introns is shown in Fig. 3b. The introns in Fig. 3b, at position 1339 to 1477 and position 1579 to 1786, relative to the translation start site, were named "intron 1" and "intron 2", respectively. The intron at position 549 to 1477 was named "intron 3". Example 3. Construction of Modified Bt ICP Genes The bt2 coding region, which has been modified in PCT publication WO 91/16432, was either the bt884 or bt860-neo coding region (Hόfte et al, 1986; Vaeck et al, 1987) . One example of such a modified bt2 coding region is the crvIAb6 coding region, which is derived from the bt884 coding region (Hόfte et al, 1986) and has been modified (with the purpose to restore the elongation efficiency) between its nucleotides 590 (Xbal site) and 917 (EcoRI site) , affecting 63 of the 107 codons within this fragment. In a similar way, the CCAAT boxes at nucleotides 772 and 789 of the bt884 coding sequence (in plasmid pJD884) are specifically removed to demonstrate that these process-directing sequence elements are involved in inhibition of transcript elongation. The oligonucleotides RVA-5 and RVA-6 are used: to modify the proximal CCAAT box by changing its A at position 774 into a G; and to modify the proximal CCAAT box by changing its A at position 792 into a G or by changing its A and T at positions 792 and 793 into a G and C, respectively. The resulting construct changed at positions 774 and 792 is called "pRVA0201", and the resulting construct changed at positions 774, 792 and 793 is called "pRVA0202". RVA-5 is a mixture of oligonucleotides of SEQ ID NO. 18 and SEQ ID NO. 19; and RVA-6 is a mixture of the oligonucleotides of SEQ ID NO. 20 and 21, that are complementary to RVA-5. - 32 - The PCR-mediated mutagenesis procedure described by Ho e al (1989) is used to incorporate the nucleotide sequences o the RVA-5 and RVA-6 fragments into a 1091 bp Spel-EcoN fragment of bt884 to change its CCAAT boxes at nucleotides 77 and 789. pRVA0201 and pRVA0202 are then introduced b electroporation into tobacco SRI protoplasts for expressio evaluation. Gene expression is found to be significantl improved. The cryptic introns in the bt884 mRNA located at position 1339-1477 (intron 1) , 1579-1786 (intron 2) and 549-1477 (intro 3), relative to the translation start site, are functionall removed by the introduction of translationally neutral bas substitutions at the appropriate positions in the bt884 coding region. The mutations are chosen such that the cryptic intron splice sites present on the bt884 coding region, which are necessary for the occurrence of splicing, become non-functional. Specifically, the 5' splice site of intron 1 was changed from AGT:GTAAGT into TCT:GTTTCG, the 5' splice site of intron 2 was changed from CGG:GTAAGA into CGT:GTCCGG, and the 5' splice site of intron 3 was changed from AAG:GTGGGG into GCG:CTGGGG. The modifications were introduced each independently into plasmid pRVA0214 chat carries the crvIAb22 gene. This gene is a derivative of bt884 that lacks the first 28 codons and has a GCU codon following the translation start signal. Furthermore, plasmid pRVA0214, which is derived from pJD884 (SEQ ID NO. 22) , carries a chimeric cat reporter gene that serves as an experimental internal control in transient expression assays (Denecke et al, 1989) . In a next step, the different 5' splice site modifications were combined resulting in a series of pRVA0214 derivatives carrying crvIAb genes with a modified 5' splice site of intron 1; intron 1 and 2; intron 1 and 3; intron 1, 2 and 3; intron 2; intron 2 and 3; and intron 3. The plasmids were introduced into SRI mesophyll protoplasts and 7 hours after delivery the expression of the different modified cry genes and of the cat gene was measured at the mRNA and protein level. An overview of the data is given in Table 1. These data show that the genes modified at the 5' splice site of intron 2 give the highest ICP expression. When combined with modification in the 5' splice sites of intron 1 and 3, ICP expression further improves. The relative ICP production rate was determined essentially as described by Denecke et al (1983, Table 2). This revealed that the splice site modifications greatly improve ICP production in time. In addition, a derivative of the crvIAbδ gene was made that carries the modified 5' splice sites of intron 2. Expression of this gene (crvIAbl4) was compared with cryIAb6 at the mRNA and protein synthesis level. As shown in Table 2, the modification of the 5' splice site of intron 2, results in increased RNA level and greatly improves the ICP production level. Taken together, these data demonstrate that the cryptic introns in b_tδ_8_4, particularly intron I and II, even more particularly intron II, cause abortive splicing of the bt884 precursor mRNA. Example 4. Cloning and Expression of Modified Bt ICP Genes in Tobacco and Potato Plants Using the procedures described in US patent application 821,582, filed January 22, 1986, and EPA 86300291.1, EPA 88402115.5 and EPA 89400428.2, the modified Bt ICP (i.e., bt2) genes of Example 3 are inserted into the intermediate T-DNA vector, pGSHllδO (Deblaere et al, 1988), between the vector's T-DNA terminal border repeat sequences. To obtain significant expression in plants, the modified Bt ICP genes of Example 3 are placed under the control of either the 35S promoter or the TR2' promoter (PTR2 - Velten et al, 1984) and are fused to the transcript 3' end formation and - 34 - polyadenylation signals of the chalcone synthase gene or the g7 gene. In addition, the translation initiation context or site is changed in accordance with the Joshi consensus sequence (Joshi, 1987) in order to optimize the translation initiation in plant cells. To this end, an oligo duplex is introduced to create the sequence, shown in SEQ ID NO. 23 from position 7561 to 6, at the translation initiation site. In this way, an additional codon (i.e., GCT) coding for alanine is introduced. Additionally, Kpnl and BstXI sites are created upstream of the ATG translation initiation codon. Using standard procedures (Deblaere et al, 1985) , the intermediate plant expression vectors, containing the modified Bt ICP gene, are transferred into the Agrobacterium strain C58C1 Rif H (US patent application 821,582; EPA 86300291.1) carrying the disarmed Ti-plasmid pGV2260 (Vaeck et al, 1987) . Selection for spectino ycin resistance yields cointegrated plasmids, consisting of pGV2260 and the respective intermediate plant expression vectors. Each of these recombinant Agrobacterium strains is then used to transform different tobacco plant cells (Nicotiana tabacum) and potato plant cells (Solanum tuberosum) so that the modified Bt ICP genes are contained in, and expressed by, different tobacco and potato plant cells. The transgenic tobacco plants containing the modified Bt ICP genes are analyzed with an ELISA assay. These plants are characterized by a significant increase in levels of Bt (bt2) proteins, compared to a transgenic tobacco plant containing a non-modified Bt ICP (bt2) gene. The insecticidal activity of the expression products of the modified Bt ICP (bt2) genes in leaves of transformed tobacco and potato plants is evaluated by recording the growth rate and mortality of larvae of tobacco hornworm (Manduca sexta) , tobacco budworm (Heliothis virescens) and potato tubermoth (Phthorimaea ooerculella) fed on leaves of these two types of plants. These results are compared with the growth rate of larvae fed leaves from tobacco and potato plants transformed with the unmodified or parental Bt ICP (bt2) gen and leaves from untransformed potato and tobacco plants. Toxicity assays are performed as described in EPA 88402115.5 and EPA 86300291.1. The insecticidal activity of transgenic tobacco plants containing the modified Bt ICP genes is determined against second and third instar larvae of Heliothis virescens . The control plants were not transformed. A significantly higher mortality rate is obtained among larvae fed on leaves of transformed plants containing and expressing the modified Bt ICP genes. Tobacco and potato plants containing the modified Bt ICP genes show considerably higher expression levels of Bt ICPs compared to tobacco and potato plants containing the unmodified Bt ICP gene. Needless to say, this invention is not limited to tobacco and potato plants transformed with the modified Bt ICP gene. It includes any plant, such as tomato, alfalfa, sunflowers, corn, cotton, soybean, sugar beets, rapeseed, brassicas and other vegetables, transformed with the modified Bt ICP gene. Nor is the invention limited to the use of Agrobacterium tumefaciens Ti-plasmids for transforming plant cells with a modified Bt ICP gene. Other known techniques for plant transformation, such as by means of liposomes, by electroporation or by vector systems based on plant viruses or pollen, can be used for transforming monocotyledonous and dicotyledonous plants with such a modified Bt ICP gene. In this regard, monocots, including economically important crops such as cereals, particularly corn and rice, can be efficiently transformed using the procedures described in WO 92/09696, in which compact embryogenic callus or intact tissue, from which such callus can be obtained, is wounded by cutting and/or enzymatic degradation and then is transformed, for example by means of electroporation of linear DNA molecules. Nor is the invention limited to the bt2 gene but rather encompasses all Cryl, Cryll, Crylll and CryIV Bt ICP genes. Indeed, sequences which can be present in cryptic promoters, e.g. CCAAT sequences, are found on both DNA strands (i.e., - 36 - coding and non-coding strands) in all Bt ICP genes. By way of example, the positions of different perfect CCAAT sequences are listed in Table 3 below for the crylB (bt!4) gene, crylC (bt!5) gene, crvIE (bt!8) gene and crvIIID (bt!09P) gene. If such CCAAT sequences are in the correct environment, they can function as a cryptic promoter and thus interfere with transcription. Similarly, plant intron splice sites are found within the coding region of many Bt ICPs. By using the properties of this invention abortive introns can be identified in these genes. Table 1 - Relative protein levels were determined by ELISA and CAT activity assays. Protein values are not absolute but rather show a general trend. The genes crylAb28, -24, -21, -26, -27, -23, and -25 are derived from the crvIAb22 gene. 38 - Table 2 - relative bt_ mRNA levels in total RNA of transiently transformed tobacco leaf protoplasts was determined 7 hrs after plasmid delivery corrected for cat mRNA levels essentially as described by Cornelissen and Vandewiele (1989b) . ΔlCP/hr is the relative ICP accumulation rate per hour corrected for the CAT accumulation rate per hour (ND: not determined) . - ICP/CAT values were determined as described in patent publication no WO 91/16432. Time point samples were taken 0, 3.5, 7, 11 and 20 hrs after plasmid delivery. RNA and protein values are not absolute but rather show a general trend. - the genes crvIAb24, 23, and .2JL are derived from crvIAb22, gene crvIAbl4 is derived from cryIAb6. Table 3 - The positions of other inhibitory sequences that can interact with CCAAT binding proteins are not listed in Table 3. References - Adang et al, Gene 36, 289-300 (1985) . - Aebi and Weismann, Trends Genet. 3, 102-107 (1988). - Benfey et al, EMBO J. 9, 1677-1684 (1990) . - Barton et al, Plant Physiol. 85, 1103-1109 (1987) . - Brown, Nucleic Acids Research 14, 9549-9559 (1986) . - Callis et al, Genes Dev. 1, 1183-1200 (1987) . - Cannon et al, Nucl. 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COUNTRY : Belgium i) CURRENT APPLICATION DATA : Not Available (vii) PRIOR APPLICATION DATA : EP 91402920.2, filed October 30, 1991 EP 92400820.4, filed March 25, 1992. 44 2. Sequence Description : SEQ ID NO. 1 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 26 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS48 CATGCTGTAC GCTGGTACAA TACGGG 26 3. Sequence Description : SEQ ID NO. 2 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS43 GGACTCCTAA TACTTCCTTC TATGCCCTG 29 4. Sequence Description : SEQ ID NO. 3 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 24 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS38 GGCGACATGG CCGCTGAGAA TCTG 24 5. Sequence Description : SEQ ID NO. 4 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 11 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS39 CAGATTCTCA G 11 6. Sequence Description : SEQ ID NO. 5 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 25 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS47 GCTGGTACAA TACGGGATTA GAGCG 25 7. Sequence Description : SEQ ID NO. 6 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 26 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS44 CCTTCTATGC CCTGAGCCGA GCCTCG 26 8. Sequence Description : SEQ ID NO. 7 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 24 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS3i GGCGACATGG CCGCTGAGAA TCTG 24 9. Sequence Description : SEQ ID NO. 8 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 26 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS46 TACGGGATTA GAGCGTGTAT GGGGAC 26 46 10. Sequence Description : SEQ ID NO. 9 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 23 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS45 GCCGAGCCTC GAAAACTACC ATC 23 11. Sequence Description : SEQ ID NO. 10 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS58 GTGCCACCTA GGCAAGGATT TAGTCATCG 29 12. Sequence Description : SEQ ID NO. 11 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS59 TAGCTCATCG GGGGATCTGC TAGAGCCGG 29 13. Sequence Description : SEQ ID NO. 12 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: 1inear MOLECULAR TYPE: oligonucieotide, designated as PS61 ACATTGCCGT AGATGAAAGA CTGAGTGCG 29 14. Sequence Description : SEQ ID NO. 13 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS62 CCCCAATCGA TATTTCCTTG TCGCTAACG 29 15. Sequence Description : SEQ ID NO. 14 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS63 TTGGACAAAG GTGGGGATTT GATGCCGCG 29 16. Sequence Description : SEQ ID NO. 15 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS64 ATCCGGTCCC CATACACGCT CTAATCCCG 29 17. Sequence Description : SEQ ID NO. 16 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS65 ATGGCTTAAT CGATGACTAA ATCCTTGCC 48 18. Sequence Description : SEQ ID NO. 17 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 29 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as PS66 CCAAATCGAT GGATCCCGAT AACAATCCG 29 19. Sequence Description : SEQ ID NO. 18 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 37 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as RVA-5a ACGTATCCGA TTCGAACAGT TTCCCAGTTA ACAAGAG 37 20. Sequence Description : SEQ ID NO. 19 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 37 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as RVA-5b ACGTATCCGA TTCGAACAGT TTCCCAGCTA ACAAGAG 37 21. Sequence Description : SEQ ID NO. 20 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 37 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as RVA-6a CTCTTGTTAA CTGGGAAACT GTTCGAATCG GATACGT 37 22. Sequence Description : SEQ ID NO. 21 SEQUENCE TYPE: nucleotide sequence SEQUENCE LENGTH: 37 nt STRANDEDNESS: single stranded TOPOLOGY: linear MOLECULAR TYPE: oligonucieotide, designated as RVA-6b CTCTTGTTAG CTGGGAAACT GTTCGAATCG GATACGT 37 50 23. Sequence Description : SEQ ID NO. 22 SEQUENCE TYPE: nucleotide sequence and corresponding amino acid sequence SEQUENCE LENGTH: 7639 bp STRANDEDNESS: double stranded TOPOLOGY: circular MOLECULAR TYPE: plasmid DNA designated as pJD884 FEATURES: - 1 - 1869 : coding region of a truncated bt2 (crvIAb) gene, also designated as the bt884 gene 1877 - 2110 : 3' regulatory sequence containing the polyadenylation site derived from Agrobacterium T-DNA gene 7 2480 - 3005 : 35S promoter sequence derived from Cauliflower mosaic virus 3006 - 3665 : coding sequence of chloramphenicol acetyl transferase gene 3666 - 4491 : 3' regulatory sequence containing the polyadenylation site derived from Agrobacterium T-DNA octopine synthase gene 5684 - 6541 : sequence complementary to the coding sequence of the beta-lactamase gene 7155 - 7639 : TR1' and TR2' promoter derived from Agrobacterium T-DNA PROPERTIES: plasmid replicable in E.coli ATG GAT CCC GAT AAC AAT CCG AAC ATC AAT GAA TGC ATT 39 MET Asp Pro Asp Asn Asn Pro Asn lie Asn Glu Cys lie 1 5 10 CCT TAT AAT TGT TTA AGT AAC CCT GAA GTA GAA GTA TTA 78 Pro Tyr Asn Cys Leu Ser Asn Pro Glu Val Glu Val Leu 15 20 25 GGT GGA GAA AGA ATA GAA ACT GGT TAC ACC CCA ATC GAT 117 Gly Gly Glu Arg lie Glu Thr Gly Tvr Thr Pro lie Asp 30 35 ATT TCC TTG TCG CTA ACG CAA TTT CTT TTG AGT GAA TTT 156 lie Ser Leu Ser Leu Thr Gin Phe Leu Leu Ser Glu Phe 40 45 50 GTT CCC GGT GCT GGA TTT GTG TTA GGA CTA GTT GAT ATA 195 Val Pro Gly Ala Gly Phe Val Leu Glv Leu Val Asp He 55 60 65 ATA TGG GGA ATT TTT GGT CCC TCT CAA TGG GAC GCA TTT 234 He Trp Gly He Phe Gly Pro Ser Gin Trp Asp Ala Phe 70 75 CTT GTA CAA ATT GAA CAG TTA ATT AAC CAA AGA ATA GAA 273 Leu Val Gin He Glu Gin Leu He Asn Gin Arg He Glu 80 85 90 GAA TTC GCT AGG AAC CAA GCC ATT TCT AGA TTA GAA GGA 312 Glu Phe Ala Arg Asn Gin Ala He Ser Arg Leu Glu Gly 95 100 CTA AGC AAT CTT TAT CAA ATT TAC GCA GAA TCT TTT AGA 351 Leu Ser Asn Leu Tyr Gin He Tyr Ala Glu Ser Phe Arg 105 110 115 GAG TGG GAA GCA GAT CCT ACT AAT CCA GCA TTA AGA GAA 390 Glu Trp Glu Ala Asp Pro Thr Asn Pro Ala Leu Arg Glu 120 125 130 GAG ATG CGT ATT CAA TTC AAT GAC ATG AAC AGT GCC CTT 429 Glu MET Arg He Gin Phe Asn Asp MET Asn Ser Ala Leu 135 140 ACA ACC GCT ATT CCT CTT TTT GCA GTT CAA AAT TAT CAA 468 Thr Thr Ala He Pro Leu Phe Ala Val Gin Asn Tyr Gin 145 150 155 GTT CCT CTT TTA TCA GTA TAT GTT CAA GCT GCA AAT TTA 507 Val Pro Leu Leu Ser Val Tyr Val Gin Ala Ala Asn Leu 160 165 CAT TTA TCA GTT TTG AGA GAT GTT TCA GTG TTT GGA CAA 546 His Leu Ser Val Leu Arg Asp Val Ser Val Phe Gly Gin 170 175 180 AGG TGG GGA TTT GAT GCC GCG ACT ATC AAT AGT CGT TAT 585 Arg Trp Gly Phe Asp Ala Ala Thr He Asn Ser Arg Tyr 185 190 195 AAT GAT TTA ACT AGG CTT ATT GGC AAC TAT ACA GAT CAT 624 Asn Asp Leu Thr Arg Leu He Gly Asn Tyr Thr Asp His 200 205 GCT GTA CGC TGG TAC AAT ACG GGA TTA GAG CGT GTA TGG 663 Ala Val Arg Trp Tyr Asn Thr Gly Leu Glu Arg Val Trp 210 215 220 GGA CCG GAT TCT AGA GAT TGG ATA AGA TAT AAT CAA TTT 702 Gly Pro Asp Ser Arg Asp Trp He Arg Tyr Asn Gin Phe 225 230 AGA AGA GAA TTA ACA CTA ACT GTA TTA GAT ATC GTT TCT 741 Arg Arg Glu Leu Thr Leu Thr Val Leu Asp He Val Ser 235 240 245 CTA TTT CCG AAC TAT GAT AGT AGA ACG TAT CCA ATT CGA 780 Leu Phe Pro Asn Tyr Asp Ser Arg Thr Tyr Pro He Arg 250 255 260 ACA GTT TCC CAA TTA ACA AGA GAA ATT TAT ACA AAC CCA 819 Thr Val Ser Gin Leu Thr Arg Glu He Tyr Thr Asn Pro 265 270 52 GTA TTA GAA AAT TTT GAT GGT AGT TTT CGA GGC TCG GCT 858 Val Leu Glu Asn Phe Asp Gly Ser Phe Arg Gly Ser Ala 275 280 285 CAG GGC ATA GAA GGA AGT ATT AGG AGT CCA CAT TTG ATG 897 Gin Gly He Glu Gly Ser He Arg Ser Pro His Leu MET 290 295 GAT ATA CTT AAC AGT ATA ACC ATC TAT ACG GAT GCT CAT 936 Asp He Leu Asn Ser He Thr He Tyr Thr Asp Ala His 300 305 310 AGA GGA GAA TAT TAT TGG TCA GGG CAT CAA ATA ATG GCT 975 Arg Gly Glu Tyr Tyr Trp Ser Glv His Gin He MET Ala 315 320 325 TCT CCT GTA GGG TTT TCG GGG CCA GAA TTC ACT TTT CCG 1014 Ser Pro Val Gly Phe Ser Gly Pro Glu Phe Thr Phe Pro 330 335 CTA TAT GGA ACT ATG GGA AAT GCA GCT CCA CAA CAA CGT 1053 Leu Tyr Gly Thr MET Glv Asn Ala Ala Pro Gin Gin Arg 340 345 350 ATT GTT GCT CAA CTA GGT CAG GGC GTG TAT AGA ACA TTA 1092 He Val Ala Gin Leu Gly Gin Gly Val Tyr Arg Thr Leu 355 360 TCG TCC ACT TTA TAT AGA AGA CCT TTT AAT ATA GGG ATA 1131 Ser Ser Thr Leu Tyr Arg Arg Pro Phe Asn He Gly He 365 370 375 AAT AAT CAA CAA CTA TCT GTT CTT GAC GGG ACA GAA TTT 1170 Asn Asn Gin Gin Leu Ser Val Leu Asp Gly Thr Glu Phe 380 385 390 GCT TAT GGA ACC TCC TCA AAT TTG CCA TCC GCT GTA TAC 1209 Ala Tyr Gly Thr Ser Ser Asn Leu Pro Ser Ala Val Tyr 395 400 AGA AAA AGC GGA ACG GTA GAT TCG CTG GAT GAA ATA CCG 1248 Arg Lys Ser Gly Thr Val Asp Ser Leu Asp Glu He Pro 405 410 415 CCA CAG AAT AAC AAC GTG CCA CCT AGG CAA GGA TTT AGT 1287 Pro Gin Asn Asn Asn Val Pro Pro Arg Gin Gly Phe Ser 420 425 CAT CGA TTA AGC CAT GTT TCA ATG TTT CGT TCA GGC TTT 1326 His Arg Leu Ser His Val Ser MET Phe Arg Ser Gly Phe 430 435 440 AGT AAT AGT AGT GTA AGT ATA ATA AGA GCT CCT ATG TTC 1365 Ser Asn Ser Ser Val Ser He He Arg Ala Pro MET Phe 445 450 455 TCT TGG ATA CAT CGT AGT GCT GAA TTT AAT AAT ATA ATT 1404 Ser Trp He His Arg Ser Ala Glu Phe Asn Asn He He 460 465 CCT TCA TCA CAA ATT ACA CAA ATA CCT TTA ACA AAA TCT 1443 Pro Ser Ser Gin He Thr Gin He Pro Leu Thr Lys Ser 470 475 480 ACT AAT CTT GGC TCT GGA ACT TCT GTC GTT AAA GGA CCA 1482 Thr Asn Leu Gly Ser Gly Thr Ser Val Val Lys Gly Pro 485 490 GGA TTT ACA GGA GGA GAT ATT CTT CGA AGA ACT TCA CCT 1521 Gly Phe Thr Gly Glv Asp He Leu Arg Arg Thr Ser Pro 495 500 505 GGC CAG ATT TCA ACC TTA AGA GTA AAT ATT ACT GCA CCA 1560 Gly Gin He Ser Thr Leu Arg Val Asn He Thr Ala Pro 510 515 520 TTA TCA CAA AGA TAT CGG GTA AGA ATT CGC TAC GCT TCT 1599 Leu Ser Gin Arg Tyr Arg Val Arg He Arg Tyr Ala Ser 525 530 ACC ACA AAT TTA CAA TTC CAT ACA TCA ATT GAC GGA AGA 1638 Thr Thr Asn Leu Gin Phe His Thr Ser He Asp Gly Arg 535 540 545 CCT ATT AAT CAG GGG AAT TTT TCA GCA ACT ATG AGT AGT 1677 Pro He Asn Gin Gly Asn Phe Ser Ala Thr MET Ser Ser 550 555 GGG AGT AAT TTA CAG TCC GGA AGC TTT AGG ACT GTA GGT 1716 Gly Ser Asn Leu Gin Ser Gly Ser Phe Arg Thr Val Gly 560 565 570 TTT ACT ACT CCG TTT AAC TTT TCA AAT GGA TCA AGT GTA 1755 Phe Thr Thr Pro Phe Asn Phe Ser Asn Gly Ser Ser Val 575 580 585 TTT ACG TTA AGT GCT CAT GTC TTC AAT TCA GGC AAT GAA 1794 Phe Thr Leu Ser Ala His Val Phe Asn Ser Gly Asn Glu 590 595 GTT TAT ATA GAT CGA ATT GAA TTT GTT CCG GCA GAA GTA 1833 Val Tyr He Asp Arg He Glu Phe Val Pro Ala Glu Val 600 605 610 ACC TTC GAC CTG CAG CCA AGC TTG CTG ATT GAT TGA CCGGATCGAT 1879 Thr Phe Asp Leu Gin Pro Ser Leu Leu He Asp 615 620 CCGGCTCTAG CAGATCCCCC GATGAGCTAA GCTAGCTATA TCATCAATTT 1929 ATGTATTACA CATAATATCG CACTCAGTCT TTCATCTACG GCAATGTACC 1979 AGCTGATATA ATCAGTTATT GAAATATTTC TGAATTTAAA CTTGCATCAA 2029 TAAATTTATG TTTTTGCTTG GACTATAATA CCTGACTTGT TATTTTATCA 2079 ATAAATATTT AAACTATATT TCTTTCAAGA TGGGAATTAA CATCTACAAA 2129 - 54 - TTGCCTTTTC TTATCGACCA TGTACGGGTA CCGAGCTCGA ATTCCTACGC 2179 AGCAGGTCTC ATCAAGACGA TCTACCCGAG TAACAATCTC CAGGAGATCA 2229 AATACCTTCC CAAGAAGGTT AAAGATGCAG TCAAAAGATT CAGGACTAAT 2279 TGCATCAAGA ACACAGAGAA AGACATATTT CTCAAGATCA GAAGTACTAT 2329 TCCAGTATGG ACGATTCAAG GCTTGCTTCA TAAACCAAGG CAAGTAATAG 2379 AGATTGGAGT CTCTAAAAAG GTAGTTCCTA CTGAATCTAA GGCCATGCAT 2429 GGAGTCTAAG ATTCAAATCG AGGATCTAAC AGAACTCGCC GTGAAGACTG 2479 GCGAACAGTT CATACAGAGT CTTTTACGAC TCAATGACAA GAAGAAAATC 2529 TTCGTCAACA TGGTGGAGCA CGACACTCTG GTCTACTCCA AAAATGTCAA 2579 AGATACAGTC TCAGAAGACC AAAGGGCTAT TGAGACTTTT CAACAAAGGA 2629 TAATTTCGGG AAACCTCCTC GGATTCCATT GCCCAGCTAT CTGTCACTTC 2679 ATCGAAAGGA CAGTAGAAAA GGAAGGTGGC TCCTACAAAT GCCATCATTG 2729 CGATAAAGGA AAGGCTATCA TTCAAGATGC CTCTGCCGAC AGTGGTCCCA 2779 AAGATGGACC CCCACCCACG AGGAGCATCG TGGAAAAAGA AGACGTTCCA 2829 ACCACGTCTT CAAAGCAAGT GGATTGATGT GACATCTCCA CTGACGTAAG 2879 GGATGACGCA CAATCCCACT ATCCTTCGCA AGACCCTTCC TCTATATAAG 2929 GAAGTTCATT TCATTTGGAG AGGACACGCT GAAATCACCA GTCTCTCTCT 2979 ATAAATCTAT CTCTCTCTCT ATAACCATGG AGAAAAAAAT CACTGGATAT 3029 ACCACCGTTG ATATATCCCA ATGGCATCGT AAAGAACATT TTGAGGCATT 3079 TCAGTCAGTT GCTCAATGTA CCTATAACCA GACCGTTCAG CTGGATATTA 3129 CGGCCTTTTT AAAGACCGTA AAGAAAAATA AGCACAAGTT TTATCCGGCC 3179 TTTATTCACA TTCTTGCCCG CCTGATGAAT GCTCATCCGG AATTCCGTAT 322 GGCAATGAAA GACGGTGAGC TGGTGATATG GGATAGTGTT CACCCTTGTT 3279 ACACCGTTTT CCATGAGCAA ACTGAAACGT TTTCATCGCT CTGGAGTGAA 3329 TACCACGACG ATTTCCGGCA GTTTCTACAC ATATATTCGC AAGATGTGGC 3379 GTGTTACGGT GAAAACCTGG CCTATTTCCC TAAAGGGTTT ATTGAGAATA 3429 TGTTTTTCGT CTCAGCCAAT CCCTGGGTGA GTTTCACCAG TTTTGATTTA 3479 AACGTGGCCA ATATGGACAA CTTCTTCGCC CCCGTTTTCA CCATGGGCAA 3529 ATATTATACG CAAGGCGACA AGGTGCTGAT GCCGCTGGCG ATTCAGGTTC 3579 ATCATGCCGT CTGTGATGGC TTCCATGTCG GCAGAATGCT TAATGAATTA 3629 CAACAGTACT GCGATGAGTG GCAGGGCGGG GCGTAATTTT TTTAAGGCAG 3679 TTATTGGTGC CCTTAAACGC CTGGTTGCTA CGCCTGAATA AGTGATAATA 372 AGCGGATGAA TGGCAGAAAT TCGAAAGCAA ATTCGACCCA TCGCGCGTCT 3779 AGAGTCCTGC TTTAATGAGA TATGCGAGAC GCCTATGATC GCATGATATT 3829 TGCTTTCAAT TCTGTTGTGC ACGTTGTAAA AAACCTGAGC ATGTGTAGCT 3879 CAGATCCTTA CCGCCGGTTT CGGTTCATTC TAATGAATAT ATCACCCGTT 3929 ACTATCGTAT TTTTATGAAT AATATTCTCC GTTCAATTTA CTGATTGTAC 3 79 CCTACTACTT ATATGTACAA TATTAAAATG AAAACAATAT ATTGTGCTGA 4029 ATAGGTTTAT AGCGACATCT ATGATAGAGC GCCACAATAA CAAACAATTG 4079 CGTTTTATTA TTACAAATCC AATTTTAAAA AAAGCGGCAG AACCGGTCAA 4129 ACCTAAAAGA CTGATTACAT AAATCTTATT CAAATTTCAA AAGGCCCCAG 4179 GGGCTAGTAT CTACGACACA CCGAGCGGCG AACTAATAAC GTTCACTGAA 4229 GGGAACTCCG GTTCCCCGCC GGCGCGCATG GGTGAGATTC CTTGAAGTTG 4279 AGTATTGGCC GTCCGCTCTA CCGAAAGTTA CGGGCACCAT TCAACCCGGT 4329 CCAGCACGGC GGCCGGGTAA CCGACTTGCT GCCCCGAGAA TTATGCAGCA 4379 TTTTTTTGGT GTATGTGGGC CCCAAATGAA GTGCAGGTCA AACCTTGACA 4429 GTGACGACAA ATCGTTGGGC GGGTCCAGGG CGAATTTTGC GACAACATGT 4479 CGAGGCTCAG CAGGACCTGC AGGAATTCGG CGTAATCATG GTCATAGCTG 4529 TTTCCTGTGT GAAATTGTTA TCCGCTCACA ATTCCACACA ACATACGAGC 4579 CGGAAGCATA AAGTGTAAAG CCTGGGGTGC CTAATGAGTG AGCTAACTCA 4629 CATTAATTGC GTTGCGCTCA CTGCCCGCTT TCCAGTCGGG AAACCTGTCG 4679 TGCCAGCTGC ATTAATGAAT CGGCCAACGC GCGGGGAGAG GCGGTTTGCG 4729 TATTGGGCGC TCTTCCGCTT CCTCGCTCAC TGACTCGCTG CGCTCGGTCG 4779 TTCGGCTGCG GCGAGCGGTA TCAGCTCACT CAAAGGCGGT AATACGGTTA 4829 TCCACAGAAT CAGGGGATAA CGCAGGAAAG AACATGTGAG CAAAAGGCCA 4879 GCAAAAGGCC AGGAACCGTA AAAAGGCCGC GTTGCTGGCG TTTTTCCATA 4929 GGCTCCGCCC CCCTGACGAG CATCACAAAA ATCGACGCTC AAGTCAGAGG 4979 TGGCGAAACC CGACAGGACT ATAAAGATAC CAGGCGTTTC CCCCTGGAAG 5029 CTCCCTCGTG CGCTCTCCTG TTCCGACCCT GCCGCTTACC GGATACCTGT 5079 CCGCCTTTCT CCCTTCGGGA AGCGTGGCGC TTTCTCAATG CTCACGCTGT 5129 AGGTATCTCA GTTCGGTGTA GGTCGTTCGC TCCAAGCTGG GCTGTGTGCA 5179 CGAACCCCCC GTTCAGCCCG ACCGCTGCGC CTTATCCGGT AACTATCGTC 5229 TTGAGTCCAA CCCGGTAAGA CACGACTTAT CGCCACTGGC AGCAGCCACT 5279 GGTAACAGGA TTAGCAGAGC GAGGTATGTA GGCGGTGCTA CAGAGTTCTT 5329 GAAGTGGTGG CCTAACTACG GCTACACTAG AAGGACAGTA TTTGGTATCT 5379 GCGCTCTGCT GAAGCCAGTT ACCTTCGGAA AAAGAGTTGG TAGCTCTTGA 5429 TCCGGCAAAC AAACCACCGC TGGTAGCGGT GGTTTTTTTG TTTGCAAGCA 5479 GCAGATTACG CGCAGAAAAA AAGGATCTCA AGAAGATCCT TTGATCTTTT 5529 CTACGGGGTC TGACGCTCAG TGGAACGAAA ACTCACGTTA AGGGATTTTG 5579 GTCATGAGAT TATCAAAAAG GATCTTCACC TAGATCCTTT TAAATTAAAA 5629 ATGAAGTTTT AAATCAATCT AAAGTATATA TGAGTAAACT TGGTCTGACA 5679 GTTACCAATG CTTAATCAGT GAGGCACCTA TCTCAGCGAT CTGTCTATTT 5729 CGTTCATCCA TAGTTGCCTG ACTCCCCGTC GTGTAGATAA CTACGATACG 5779 GGAGGGCTTA CCATCTGGCC CCAGTGCTGC AATGATACCG CGAGACCCAC 5829 GCTCACCGGC TCCAGATTTA TCAGCAATAA ACCAGCCAGC CGGAAGGGCC 5879 GAGCGCAGAA GTGGTCCTGC AACTTTATCC GCCTCCATCC AGTCTATTAA 5929 TTGTTGCCGG GAAGCTAGAG TAAGTAGTTC GCCAGTTAAT AGTTTGCGCA 5979 ACGTTGTTGC CATTGCTACA GGCATCGTGG TGTCACGCTC GTCGTTTGGT 6029 ATGGCTTCAT TCAGCTCCGG TTCCCAACGA TCAAGGCGAG TTACATGATC 6079 CCCCATGTTG TGCAAAAAAG CGGTTAGCTC CTTCGGTCCT CCGATCGTTG 6129 TCAGAAGTAA GTTGGCCGCA GTGTTATCAC TCATGGTTAT GGCAGCACTG 6179 CATAATTCTC TTACTGTCAT GCCATCCGTA AGATGCTTTT CTGTGACTGG 6229 TGAGTACTCA ACCAAGTCAT TCTGAGAATA GTGTATGCGG CGACCGAGTT 6279 GCTCTTGCCC GGCGTCAATA CGGGATAATA CCGCGCCACA TAGCAGAACT 6329 TTAAAAGTGC TCATCATTGG AAAACGTTCT TCGGGGCGAA AACTCTCAAG 6379 GATCTTACCG CTGTTGAGAT CCAGTTCGAT GTAACCCACT CGTGCACCCA 6429 ACTGATCTTC AGCATCTTTT ACTTTCACCA GCGTTTCTGG GTGAGCAAAA 6479 ACAGGAAGGC AAAATGCCGC AAAAAAGGGA ATAAGGGCGA CACGGAAATG 6529 TTGAATACTC ATACTCTTCC TTTTTCAATA TTATTGAAGC ATTTATCAGG 6579 GTTATTGTCT CATGAGCGGA TACATATTTG AATGTATTTA GAAAAATAAA 6629 CAAATAGGGG TTCCGCGCAC ATTTCCCCGA AAAGTGCCAC CTGACGTCTA 6679 AGAAACCATT ATTATCATGA CATTAACCTA TAAAAATAGG CGTATCACGA 6729 GGCCCTTTCG TCTCGCGCGT TTCGGTGATG ACGGTGAAAA CCTCTGACAC 6779 ATGCAGCTCC CGGAGACGGT CACAGCTTGT CTGTAAGCGG ATGCCGGGAG 6829 CAGACAAGCC CGTCAGGGCG CGTCAGCGGG TGTTGGCGGG TGTCGGGGCT 6879 GGCTTAACTA TGCGGCATCA GAGCAGATTG TACTGAGAGT GCACCATATG 6929 CGGTGTGAAA TACCGCACAG ATGCGTAAGG AGAAAATACC GCATCAGGCG 6979 CCATTCGCCA TTCAGGCTGC GCAACTGTTG GGAAGGGCGA TCGGTGCGGG 7029 CCTCTTCGCT ATTACGCCAG CTGGCGAAAG GGGGATGTGC TGCAAGGCGA 7079 TTAAGTTGGG TAACGCCAGG GTTTTCCCAG TCACGACGTT GTAAAACGAC 7129 GGCCAGTAAG CTTGGCTGCA GGTCGAGATC CACGTGTGGA AGATATGAAT 7179 TTTTTTGAGA AACTAGATAA GATTAATGAA TATCGGTGTT TTGGTTTTTT 7229 CTTGTGGCCG TCTTTGTTTA TATTGAGATT TTTCAAATCA GTGCGCAAGA 7279 CGTGACGTAA GTATCTGAGC TAGTTTTTAT TTTTCTACTA ATTTGGTCGT 7329 TTATTTCGGC GTGTAGGACA TGGCAACCGG GCCTGAATTT CGCGGGTATT 7379 CTGTTTCTAT TCCAACTTTT TCTTGATCCG CAGCCATTAA CGACTTTTGA 7429 ATAGATACGC TGACACGCCA AGCCTCGCTA GTCAAAAGTG TACCAAACAA 7479 CGCTTTACAG CAAGAACGGA ATGCGCGTGA CGCTCGCGGT GACGCCATTT 7529 CGCCTTTTCA GAAATGGATA AATAGCCTTG CTTCCTATTA TATCTTCCCA 7579 AATTACCAAT ACATTACACT AGCATCTGAA TTTCATAACC AATCTCGATA 7629 CACCAAATCG 7639 24. Sequence Description : SEQ ID NO. 23 SEQUENCE TYPE: nucleotide sequence and corresponding amino acid sequence SEQUENCE LENGTH: 7566 bp STRANDEDNESS: double-stranded TOPOLOGY: circular MOLECULAR TYPE: plasmid DNA designated as pPS0212 FEATURES: - 1 - 1785 : coding region of a truncated modified bt2 (crvIAb) gene, also designated as the crylAbβ gene 1793 - 2026 : 3' regulatory sequence containing the polyadenylation site derived from Agrobacterium T-DNA gene 7 2396 - 2921 : 35S promoter sequence derived from Cauliflower mosaic virus 2922 - 3581 : coding sequence of chloramphenicol acetyl transferase gene 3582 - 4407 : 3' regulatory sequence containing the polyadenylation site derived from Agrobacterium T-DNA octopine synthase gene 5600 - 6457 : sequence complementary to the coding sequence of the beta-lactamase gene 7071 - 7566 : TR1' and TR2' promoter derived from Agrobacterium T-DNA (with modified leader with respect to sequence of pJD884 of SEQ ID NO. 22 PROPERTIES: plasmid replicable in E.coli. ATG GCT ATC GAG ACC GGT TAC ACC CCA ATC GAT ATT TCC 39 MET Ala He Glu Thr Gly Tyr Thr Pro He Asp He Ser 1 5 10 TTG TCG CTA ACG CAA TTT CTT TTG AGT GAA TTT GTT CCC 78 Leu Ser Leu Thr Gin Phe Leu Leu Ser Glu Phe Val Pro 15 20 25 GGT GCT GGA TTT GTG TTA GGA CTA GTT GAT ATA ATA TGG 117 Gly Ala Gly Phe Val Leu Gly Leu Val Asp He He Trp 30 35 GGA ATT TTT GGT CCC TCT CAA TGG GAC GCA TTT CTT GTA 156 Gly He Phe Gly Pro Ser Gin Trp Asp Ala Phe Leu Val 40 45 50 CAA ATT GAA CAG TTA ATT AAC CAA AGA ATA GAA GAA TTC 195 Gin He Glu Gin Leu He Asn Gin Arg He Glu Glu Phe 55 60 65 GCT AGG AAC CAA GCC ATT TCT AGA TTA GAA GGA CTA AGC 234 Ala Arg Asn Gin Ala He Ser Arg Leu Glu Gly Leu Ser 70 75 AAT CTT TAT CAA ATT TAC GCA GAA TCT TTT AGA GAG TGG 273 Asn Leu Tyr Gin He Tyr Ala Glu Ser Phe Arg Glu Trp 80 85 90 GAA GCA GAT CCT ACT AAT CCA GCA TTA AGA GAA GAG ATG 312 Glu Ala Asp Pro Thr Asn Pro Ala Leu Arg Glu Glu MET 95 100 CGT ATT CAA TTC AAT GAC ATG AAC AGT GCC CTT ACA ACC 351 Arg He Gin Phe Asn Asp MET Asn Ser Ala Leu Thr Thr 105 110 115 GCT ATT CCT CTT TTT GCA GTT CAA AAT TAT CAA GTT CCT 390 Ala He Pro Leu Phe Ala Val Gin Asn Tyr Gin Val Pro 120 125 130 CTT TTA TCA GTA TAT GTT CAA GCT GCA AAT TTA CAT TTA 429 Leu Leu Ser Val Tyr Val Gin Ala Ala Asn Leu His Leu 135 140 TCA GTT TTG AGA GAT GTT TCA GTG TTT GGA CAA AGG TGG 468 Ser Val Leu Arg Asp Val Ser Val Phe Gly Gin Arg Trp 145 150 155 GGA TTT GAT GCC GCG ACT ATC AAT AGT CGT TAT AAT GAT 507 Gly Phe Asp Ala Ala Thr He Asn Ser Arg Tyr Asn Asp 160 165 TTA ACT AGG CTT ATT GGC AAC TAT ACA GAT CAT GCT GTA 546 Leu Thr Arg Leu He Gly Asn Tyr Thr Asp His Ala Val 170 175 180 CGC TGG TAC AAT ACG GGA TTA GAG CGT GTA TGG GGA CCG 585 Arg Trp Tyr Asn Thr Gly Leu Glu Arg Val Trp Gly Pro 185 190 195 GAT TCT AGA GAC TGG ATC AGG TAC AAC CAG TTC AGG AGG 624 Asp Ser Arg Asp Trp He Arg Tyr Asn Gin Phe Arg Arg 200 205 GAG TTA ACC CTA ACC GTG TTA GAC ATC GTG TCC CTA TTC 663 Glu Leu Thr Leu Thr Val Leu Asp He Val Ser Leu Phe 210 215 220 CCG AAC TAC GAC AGC AGG ACG TAC CCA ATC CGA ACC GTG 702 Pro Asn Tyr Asp Ser Arg Thr Tyr Pro He Arg Thr Val 225 230 TCC CAG TTA ACC AGG GAG ATC TAC ACC AAC CCA GTG TTA 741 Ser Gin Leu Thr Arg Glu He Tyr Thr Asn Pro Val Leu 235 240 245 GAG AAC TTC GAC GGT AGC TTC CGA GGC TCG GCT CAG GGC 780 Glu Asn Phe Asp Gly Ser Phe Arg Gly Ser Ala Gin Gly 250 255 260 ATC GAG GGA AGC ATC AGG AGC CCA CAC TTG ATG GAC ATC 819 He Glu Gly Ser He Arg Ser Pro His Leu MET Asp He 265 270 58 CTT AAC AGC ATC ACC ATC TAC ACG GAC GCT CAC AGG GGA 858 Leu Asn Ser He Thr He Tyr Thr Asp Ala His Arg Gly 275 280 285 GAG TAC TAC TGG TCC GGG CAC CAG ATC ATG GCT TCC CCT 897 Glu Tyr Tvr Trp Ser Gly His Gin He MET Ala Ser Pro 290 295 GTG GGG TTC TCG GGG CCA GAA TTC ACT TTT CCG CTA TAT 936 Val Glv Phe Ser Gly Pro Glu Phe Thr Phe Pro Leu Tyr 300 ~ 305 310 GGA ACT ATG GGA AAT GCA GCT CCA CAA CAA CGT ATT GTT 975 Gly Thr MET Gly Asn Ala Ala Pro Gin Gin Arg He Val 315 320 325 GCT CAA CTA GGT CAG GGC GTG TAT AGA ACA TTA TCG TCC 1014 Ala Gin Leu Gly Gin Gly Val Tyr Arg Thr Leu Ser Ser 330 335 ACT TTA TAT AGA AGA CCT TTT AAT ATA GGG ATA AAT AAT 1053 Thr Leu Tyr Arg Arg Pro Phe Asn He Gly He Asn Asn 340 345 350 CAA CAA CTA TCT GTT CTT GAC GGG ACA GAA TTT GCT TAT 1092 Gin Gin Leu Ser Val Leu Asp Gly Thr Glu Phe Ala Tyr 355 360 GGA ACC TCC TCA AAT TTG CCA TCC GCT GTA TAC AGA AAA 1131 Gly Thr Ser Ser Asn Leu Pro Ser Ala Val Tyr Arg Lys 365 370 375 AGC GGA ACG GTA GAT TCG CTG GAT GAA ATA CCG CCA CAG 1170 Ser Gly Thr Val Asp Ser Leu Asp Glu He Pro Pro Gin 380 385 390 AAT AAC AAC GTG CCA CCT AGG CAA GGA TTT AGT CAT CGA 1209 Asn Asn Asn Val Pro Pro Arg Gin Gly Phe Ser His Arg 395 400 TTA AGC CAT GTT TCA ATG TTT CGT TCA GGC TTT AGT AAT 1248 Leu Ser His Val Ser MET Phe Arg Ser Gly Phe Ser Asn 405 410 415 AGT AGT GTA AGT ATA ATA AGA GCT CCT ATG TTC TCT TGG 1287 Ser Ser Val Ser He He Arg Ala Pro MET Phe Ser Trp 420 425 ATA CAT CGT AGT GCT GAA TTT AAT AAT ATA ATT CCT TCA 1326 He His Arg Ser Ala Glu Phe Asn Asn He He Pro Ser 430 435 440 TCA CAA ATT ACA CAA ATA CCT TTA ACA AAA TCT ACT AAT 1365 Ser Gin He Thr Gin He Pro Leu Thr Lys Ser Thr Asn 445 450 455 CTT GGC TCT GGA ACT TCT GTC GTT AAA GGA CCA GGA TTT 1404 Leu Gly Ser Gly Thr Ser Val Val Lys Gly Pro Gly Phe 460 465 ACA GGA GGA GAT ATT CTT CGA AGA ACT TCA CCT GGC CAG 1443 Thr Gly Gly Asp He Leu Arg Arg Thr Ser Pro Gly Gin 470 475 480 ATT TCA ACC TTA AGA GTA AAT ATT ACT GCA CCA TTA TCA 1482 He Ser Thr Leu Arg Val Asn He Thr Ala Pro Leu Ser 485 490 CAA AGA TAT CGG GTA AGA ATT CGC TAC GCT TCT ACC ACA 1521 Gin Arg Tyr Arg Val Arg He Arg Tyr Ala Ser Thr Thr 495 500 505 AAT TTA CAA TTC CAT ACA TCA ATT GAC GGA AGA CCT ATT 1560 Asn Leu Gin Phe His Thr Ser He Asp Gly Arg Pro He 510 515 520 AAT CAG GGG AAT TTT TCA GCA ACT ATG AGT AGT GGG AGT 1599 Asn Gin Gly Asn Phe Ser Ala Thr MET Ser Ser Gly Ser 525 530 AAT TTA CAG TCC GGA AGC TTT AGG ACT GTA GGT TTT ACT 1638 Asn Leu Gin Ser Gly Ser Phe Arg Thr Val Gly Phe Thr 535 540 545 ACT CCG TTT AAC TTT TCA AAT GGA TCA AGT GTA TTT ACG 1677 Thr Pro Phe Asn Phe Ser Asn Gly Ser Ser Val Phe Thr 550 555 TTA AGT GCT CAT GTC TTC AAT TCA GGC AAT GAA GTT TAT 1716 Leu Ser Ala His Val Phe Asn Ser Gly Asn Glu Val Tyr 560 565 570 ATA GAT CGA ATT GAA TTT GTT CCG GCA GAA GTA ACC TTC 1755 He Asp Arg He Glu Phe Val Pro Ala Glu Val Thr Phe 575 580 585 GAC CTG CAG CCA AGC TTG CTG ATT GAT TGA CCGGATCGAT 1795 Asp Leu Gin Pro Ser Leu Leu He Asp 590 595 CCGGCTCTAG CAGATCCCCC GATGAGCTAA GCTAGCTATA TCATCAATTT 1845 ATGTATTACA CATAATATCG CACTCAGTCT TTCATCTACG GCAATGTACC 1895 AGCTGATATA ATCAGTTATT GAAATATTTC TGAATTTAAA CTTGCATCAA 1945 TAAATTTATG TTTTTGCTTG GACTATAATA CCTGACTTGT TATTTTATCA 1995 ATAAATATTT AAACTATATT TCTTTCAAGA TGGGAATTAA CATCTACAAA 2045 TTGCCTTTTC TTATCGACCA TGTACGGGTA CCGAGCTCGA ATTCCTACGC 2095 AGCAGGTCTC ATCAAGACGA TCTACCCGAG TAACAATCTC CAGGAGATCA 2145 AATACCTTCC CAAGAAGGTT AAAGATGCAG TCAAAAGATT CAGGACTAAT 2195 TGCATCAAGA ACACAGAGAA AGACATATTT CTCAAGATCA GAAGTACTAT 2245 TCCAGTATGG ACGATTCAAG GCTTGCTTCA TAAACCAAGG CAAGTAATAG 2295 AGATTGGAGT CTCTAAAAAG GTAGTTCCTA CTGAATCTAA GGCCATGCAT 2345 GGAGTCTAAG ATTCAAATCG AGGATCTAAC AGAACTCGCC GTGAAGACTG 2395 GCGAACAGTT CATACAGAGT CTTTTACGAC TCAATGACAA GAAGAAAATC 2445 TTCGTCAACA TGGTGGAGCA CGACACTCTG GTCTACTCCA AAAATGTCAA 2495 AGATACAGTC TCAGAAGACC AAAGGGCTAT TGAGACTTTT CAACAAAGGA 2545 TAATTTCGGG AAACCTCCTC GGATTCCATT GCCCAGCTAT CTGTCACTTC 2595 ATCGAAAGGA CAGTAGAAAA GGAAGGTGGC TCCTACAAAT GCCATCATTG 2645 CGATAAAGGA AAGGCTATCA TTCAAGATGC CTCTGCCGAC AGTGGTCCCA 2695 AAGATGGACC CCCACCCACG AGGAGCATCG TGGAAAAAGA AGACGTTCCA 2745 ACCACGTCTT CAAAGCAAGT GGATTGATGT GACATCTCCA CTGACGTAAG 2795 GGATGACGCA CAATCCCACT ATCCTTCGCA AGACCCTTCC TCTATATAAG 2845 GAAGTTCATT TCATTTGGAG AGGACACGCT GAAATCACCA GTCTCTCTCT 2895 ATAAATCTAT CTCTCTCTCT ATAACCATGG AGAAAAAAAT CACTGGATAT 2945 ACCACCGTTG ATATATCCCA ATGGCATCGT AAAGAACATT TTGAGGCATT 2995 TCAGTCAGTT GCTCAATGTA CCTATAACCA GACCGTTCAG CTGGATATTA 3045 CGGCCTTTTT AAAGACCGTA AAGAAAAATA AGCACAAGTT TTATCCGGCC 3095 TTTATTCACA TTCTTGCCCG CCTGATGAAT GCTCATCCGG AATTCCGTAT 3145 GGCAATGAAA GACGGTGAGC TGGTGATATG GGATAGTGTT CACCCTTGTT 3195 ACACCGTTTT CCATGAGCAA ACTGAAACGT TTTCATCGCT CTGGAGTGAA 3245 TACCACGACG ATTTCCGGCA GTTTCTACAC ATATATTCGC AAGATGTGGC 3295 GTGTTACGGT GAAAACCTGG CCTATTTCCC TAAAGGGTTT ATTGAGAATA 3345 TGTTTTTCGT CTCAGCCAAT CCCTGGGTGA GTTTCACCAG TTTTGATTTA 3395 AACGTGGCCA ATATGGACAA CTTCTTCGCC CCCGTTTTCA CCATGGGCAA 3445 ATATTATACG CAAGGCGACA AGGTGCTGAT GCCGCTGGCG ATTCAGGTTC 3495 ATCATGCCGT CTGTGATGGC TTCCATGTCG GCAGAATGCT TAATGAATTA 3545 CAACAGTACT GCGATGAGTG GCAGGGCGGG GCGTAATTTT TTTAAGGCAG 3595 TTATTGGTGC CCTTAAACGC CTGGTTGCTA CGCCTGAATA AGTGATAATA 3645 AGCGGATGAA TGGCAGAAAT TCGAAAGCAA ATTCGACCCA TCGCGCGTCT 3695 AGAGTCCTGC TTTAATGAGA TATGCGAGAC GCCTATGATC GCATGATATT 3745 TGCTTTCAAT TCTGTTGTGC ACGTTGTAAA AAACCTGAGC ATGTGTAGCT 3795 CAGATCCTTA CCGCCGGTTT CGGTTCATTC TAATGAATAT ATCACCCGTT 3845 ACTATCGTAT TTTTATGAAT AATATTCTCC GTTCAATTTA CTGATTGTAC 3895 CCTACTACTT ATATGTACAA TATTAAAATG AAAACAATAT ATTGTGCTGA 3945 ATAGGTTTAT AGCGACATCT ATGATAGAGC GCCACAATAA CAAACAATTG 3995 CGTTTTATTA TTACAAATCC AATTTTAAAA AAAGCGGCAG AACCGGTCAA 4045 ACCTAAAAGA CTGATTACAT AAATCTTATT CAAATTTCAA AAGGCCCCAG 4095 GGGCTAGTAT CTACGACACA CCGAGCGGCG AACTAATAAC GTTCACTGAA 4145 GGGAACTCCG GTTCCCCGCC GGCGCGCATG GGTGAGATTC CTTGAAGTTG 4195 AGTATTGGCC GTCCGCTCTA CCGAAAGTTA CGGGCACCAT TCAACCCGGT 4245 CCAGCACGGC GGCCGGGTAA CCGACTTGCT GCCCCGAGAA TTATGCAGCA 4295 TTTTTTTGGT GTATGTGGGC CCCAAATGAA GTGCAGGTCA AACCTTGACA 4345 GTGACGACAA ATCGTTGGGC GGGTCCAGGG CGAATTTTGC GACAACATGT 4395 CGAGGCTCAG CAGGACCTGC AGGAATTCGG CGTAATCATG GTCATAGCTG 4445 TTTCCTGTGT GAAATTGTTA TCCGCTCACA ATTCCACACA ACATACGAGC 4495 CGGAAGCATA AAGTGTAAAG CCTGGGGTGC CTAATGAGTG AGCTAACTCA 4545 CATTAATTGC GTTGCGCTCA CTGCCCGCTT TCCAGTCGGG AAACCTGTCG 4595 TGCCAGCTGC ATTAATGAAT CGGCCAACGC GCGGGGAGAG GCGGTTTGCG 4645 TATTGGGCGC TCTTCCGCTT CCTCGCTCAC TGACTCGCTG CGCTCGGTCG 4695 TTCGGCTGCG GCGAGCGGTA TCAGCTCACT CAAAGGCGGT AATACGGTTA 4745 TCCACAGAAT CAGGGGATAA CGCAGGAAAG AACATGTGAG CAAAAGGCCA 4795 GCAAAAGGCC AGGAACCGTA AAAAGGCCGC GTTGCTGGCG TTTTTCCATA 4845 GGCTCCGCCC CCCTGACGAG CATCACAAAA ATCGACGCTC AAGTCAGAGG 4895 TGGCGAAACC CGACAGGACT ATAAAGATAC CAGGCGTTTC CCCCTGGAAG 4945 CTCCCTCGTG CGCTCTCCTG TTCCGACCCT GCCGCTTACC GGATACCTGT 4995 CCGCCTTTCT CCCTTCGGGA AGCGTGGCGC TTTCTCAATG CTCACGCTGT 5045 AGGTATCTCA GTTCGGTGTA GGTCGTTCGC TCCAAGCTGG GCTGTGTGCA 5095 CGAACCCCCC GTTCAGCCCG ACCGCTGCGC CTTATCCGGT AACTATCGTC 5145 TTGAGTCCAA CCCGGTAAGA CACGACTTAT CGCCACTGGC AGCAGCCACT 5195 GGTAACAGGA TTAGCAGAGC GAGGTATGTA GGCGGTGCTA CAGAGTTCTT 5245 GAAGTGGTGG CCTAACTACG GCTACACTAG AAGGACAGTA TTTGGTATCT 5295 5345 5395 GCAGATTACG CGCAGAAAAA AAGGATCTC AGAAGATCCT TTGATCTTTT 5445 CTACGGGGTC TGACGCTCAG TGGAACGAAA ACTCACGTTA AGGGATTTTG 5495 GTCATGAGAT TATCAAAAAG GATCTTCACC TAGATCCTTT TAAATTAAAA 5545 ATGAAGTTTT AAATCAATCT AAAGTATATA TGAGTAAACT TGGTCTGACA 5595 GTTACCAATG CTTAATCAGT GAGGCACCTA TCTCAGCGAT CTGTCTATTT 5645 CGTTCATCCA TAGTTGCCTG ACTCCCCGTC GTGTAGATAA CTACGATACG 5695 GGAGGGCTTA CCATCTGGCC CCAGTGCTGC AATGATACCG CGAGACCCAC 5745 GCTCACCGGC TCCAGATTTA TCAGCAATAA ACCAGCCAGC CGGAAGGGCC 5795 GAGCGCAGAA GTGGTCCTGC AACTTTATCC GCCTCCATCC AGTCTATTAA 5845 TTGTTGCCGG GAAGCTAGAG TAAGTAGTTC GCCAGTTAAT AGTTTGCGCA 5895 ACGTTGTTGC CATTGCTACA GGCATCGTGG TGTCACGCTC GTCGTTTGGT 5945 ATGGCTTCAT TCAGCTCCGG TTCCCAACGA TCAAGGCGAG TTACATGATC 5995 CCCCATGTTG TGCAAAAAAG CGGTTAGCTC CTTCGGTCCT CCGATCGTTG 6045 TCAGAAGTAA GTTGGCCGCA GTGTTATCAC TCATGGTTAT GGCAGCACTG 6095 CATAATTCTC TTACTGTCAT GCCATCCGTA AGATGCTTTT CTGTGACTGG 6145 TGAGTACTCA ACCAAGTCAT TCTGAGAATA GTGTATGCGG CGACCGAGTT 6195 GCTCTTGCCC GGCGTCAATA CGGGATAATA CCGCGCCACA TAGCAGAACT . 6245 TTAAAAGTGC TCATCATTGG AAAACGTTCT TCGGGGCGAA AACTCTCAAG 6295 GATCTTACCG CTGTTGAGAT CCAGTTCGAT GTAACCCACT CGTGCACCCA 6345 ACTGATCTTC AGCATCTTTT ACTTTCACCA GCGTTTCTGG GTGAGCAAAA 63 95 ACAGGAAGGC AAAATGCCGC AAAAAAGGGA ATAAGGGCGA CACGGAAATG 6445 TTGAATACTC ATACTCTTCC TTTTTCAATA TTATTGAAGC ATTTATCAGG 6495 GTTATTGTCT CATGAGCGGA TACATATTTG AATGTATTTA GAAAAATAAA 6545 CAAATAGGGG TTCCGCGCAC ATTTCCCCGA AAAGTGCCAC CTGACGTCTA 6595 AGAAACCATT ATTATCATGA CATTAACCTA TAAAAATAGG CGTATCACGA 6645 GGCCCTTTCG TCTCGCGCGT TTCGGTGATG ACGGTGAAAA CCTCTGACAC 6695 ATGCAGCTCC CGGAGACGGT CACAGCTTGT CTGTAAGCGG ATGCCGGGAG 6745 CAGACAAGCC CGTCAGGGCG CGTCAGCGGG TGTTGGCGGG TGTCGGGGCT 6795 GGCTTAACTA TGCGGCATCA GAGCAGATTG TACTGAGAGT GCACCATATG 6845 CGGTGTGAAA TACCGCACAG ATGCGTAAGG AGAAAATACC GCATCAGGCG 6895 CCATTCGCCA TTCAGGCTGC GCAACTGTTG GGAAGGGCGA TCGGTGCGGG 6945 CCTCTTCGCT ATTACGCCAG CTGGCGAAAG GGGGATGTGC TGCAAGGCGA 6995 TTAAGTTGGG TAACGCCAGG GTTTTCCCAG TCACGACGTT GTAAAACGAC 7045 GGCCAGTAAG CTTGGCTGCA GGTCGAGATC CACGTGTGGA AGATATGAAT 7095 TTTTTTGAGA AACTAGATAA GATTAATGAA TATCGGTGTT TTGGTTTTTT 7145 CTTGTGGCCG TCTTTGTTTA TATTGAGATT TTTCAAATCA GTGCGCAAGA 7195 CGTGACGTAA GTATCTGAGC TAGTTTTTAT TTTTCTACTA ATTTGGTCGT 7245 TTATTTCGGC GTGTAGGACA TGGCAACCGG GCCTGAATTT CGCGGGTATT 7295 CTGTTTCTAT TCCAACTTTT TCTTGATCCG CAGCCATTAA CGACTTTTGA 7345 ATAGATACGC TGACACGCCA AGCCTCGCTA GTCAAAAGTG TACCAAACAA 7395 CGCTTTACAG CAAGAACGGA ATGCGCGTGA CGCTCGCGGT GACGCCATTT 7445 CGCCTTTTCA GAAATGGATA AATAGCCTTG CTTCCTATTA TATCTTCCCA 7495 AATTACCAAT ACATTACACT AGCATCTGAA TTTCATAACC AATCTCGATA 7545 CACCAAATCG GTACCAAAAC C 7566

Claims: Claims 1. A process for modifying a gene, preferably a Bt ICP gene, particularly a cryl gene or a crylll gene, quite particularly a crvIAb gene, to be expressed in a plant cell transformed with the gene; the process comprises the following step: inactivating, preferably destroying or removing, in the coding region of said gene, at least one of the following process-directing sequence elements: i) a cryptic promoter, such as a minimal promoter, in either a sense or anti-sense orientation, which can direct site-specific transcription initiation in said plant cell by partial or complete assembly of an RNA polymerase II initiation complex; said cryptic promoter preferably containing a DNA regulatory element, such as a CCAAT sequence or a TATA sequence, or, ii) a DNA encoding an abortive intron that, at the RNA level, causes entry of a precursor mRNA species in a splicing pathway, said precursor mRNA species being processed by said plant cell in such a way that the resulting mRNA species does not accumulate substantially in the cytoplasm of said plant cell. 2. The process of claim 1 wherein said process-directing sequence element is inactivated by introducing translationally neutral modifications in the coding region of said gene, preferably by : a) introducing in the coding region a DNA encoding an intron, efficiently spliced in the plant cell and/or b) changing amino acid codons in the coding region with other codons encoding the same amino acids. 3. The process of claim 1 or 2 wherein said gene encodes a truncated Bt insecticidal crystal protein, preferably truncated at both its C-terminal and N-terminal ends, and wherein said gene preferably encodes a portion of said protein of about - 80 kDa, particularly the toxin of said protein. 4. The process of any one of claims 1-3, wherein said gene further modified by exchanging its ATG translation initiati context by the sequence AAAACCATGGCT. 5. The process of any one of claims 1-4, wherein said gene i a cryl gene, such as a bt2, bt884, crylAbδ, cryIAb22, bt!4 bt!5 or btlδ gene, preferably a bt2, bt884, crvIAb22, cryIAb6 gene or a gene having substantial sequence homolo thereto. 6. The process of claim 5 wherein said gene is a bt2, bt884 or cryIAb22 gene and wherein a cryptic promoter is inactivate preferably by translationally neutral modifications in th region corresponding to the region in the bt884 gene betwee nucleotides 742 and 813. 7. The process of claim 5 or 6 wherein said gene is a bt2 bt884, cryIAb22, or crylAbδ gene and wherein abortive intron are inactivated preferably by translationally neutra modifications around some or all of the 5' abortive splic sites, particularly by translationally neutral modifications i at least one of the following sequences AAG:GTGGGG, AGHGTAAGT and CGG:GTAAGA. 8. The modified gene, preferably the modified Bt ICP gene particularly the modified cryl gene, quite particularly th cryIAbl4 gene, obtained by the process of any one of claim 1-7. 9. The modified gene of claim 8, wherein less than 10%, preferably less than 3%, of the nucleotides in the codin region are modified, particularly wherein less than 10 %, preferably less than 3% of the nucleotides in the coding regio are changed from A and T nucleotides to G or C nucleotides. - 64 - 10. A chimaeric gene for transforming a cell of a plant, comprising the following operably-linked DNA fragments in the same transcriptional unit: a) the coding region of said modified gene of any one of claims 8 or 9; b) a promoter capable of directing expression of said modified gene in said plant cell; and c) transcript 3' end formation and polyadenylation signals suitable for expressing said modified gene in said plant cell, particularly that of the chalcone synthase gene. 11. The chimaeric gene of claim 10, wherein said modified gene is a modified Bt ICP gene and wherein said promoter is the 35S promoter, the TRl' promoter, or the TR2' promoter, and wherein said transcript 3' end formation and polyadenylation signal is from the chalcone synthase gene. 12. The chimaeric gene of claim 10, wherein said modified gene is a modified bt2 of claim 6 or 7, with 28 N-terminal codons deleted, wherein said promoter is the 35S promoter, the TRl' promoter, or the TR2' promoter, and wherein said transcript 3' end formation and polyadenylation signal is from the chalcone synthase gene. 13. A plant cell, transformed with the chimaeric gene of any one of claims 10-12. 14. A plant, plant tissue or plant cell culture consisting essentially of the plant cells of claim 13. 15. A seed of the plant of claim 14. 16. A vector, preferably a Ti-plasmid, for stably transforming the nuclear genome of a plant, comprising the chimaeric gene of any one of claims 10-12. 17. A process for protecting the plant of claim 14 from an insect pest, comprising the step of: transforming the genome of the plant with the chimaeric gene of any one of claims 10-12, when such modified gene is a Bt ICP gene.

Inventors: CORNELISSEN MARC, DOCKX JAN, SOETAERT PIET, STAM MAIKE, VAN AARSSEN ROEL, CORNELISSEN, MARC, DOCKX, JAN, SOETAERT, PIET, STAM, MAIKE, VAN AARSSEN, ROEL
Applicants: PLANT GENETIC SYSTEMS NV, PLANT GENETIC SYSTEMS, N.V.
Application year: 1992
Main classification: C12N5
IPC codes: A01H5, C07K14, C12N5, C12N15