Bacillus thuringiensis var. israelensis delta-endotoxin. Cloning and expression of the toxin in sporogenic and asporogenic strains of Bacillus subtilis

Preliminary X-ray diffraction analysis of crystals of Bacillus thuringiensis toxin, a cell membrane disrupting protein

Crystals suitable for high resolution X-ray diffraction analysis have been reproducibly grown of the 24,000 Mr protein insect toxin from Bacillus thuringiensis. This protein, which demonstrates substantial insecticidal activity by inserting into phospholipid membranes, crystallizes as long square needles from polyethylene glycol 4000 at neutral pH. The crystals are of space group P4(1) and have cell dimensions of a = b = 33 A and c = 235 A, which suggests to us a predominantly helical motif for the protein's structure.

Expression in Escherichia coli of a cloned crystal protein gene of Bacillus thuringiensis subsp. israelensis

A ca. 10-kilobase (kb) HindIII fragment of plasmid DNA from Bacillus thuringiensis subsp. israelensis was cloned into plasmid pUC9 and transformed into Escherichia coli. Extracts of the recombinant strain contained a 27-kilodalton (kDa) peptide that reacted with antibodies to a 27-kDa peptide isolated from crystals produced by B. thuringiensis subsp. israelensis. Extracts of the recombinant strain were hemolytic and toxic to Aedes aegypti larvae. Full expression of the 27-kDa peptide required the presence of a ca. 0.8-kb region of DNA located 4 kb upstream from the structural gene; the 0.8-kb region could be present in cis or trans relative to the gene and apparently acted post-transcriptionally. Analysis of maxicells showed that the 10-kb insert also coded for peptides of 67, 20, and 16 kDa; data obtained with different subclones suggest that the 20-kDa peptide is encoded in the 0.8-kb DNA region.

Bacillus thuringiensis var. israelensis delta-endotoxin. Nucleotide sequence and characterization of the transcripts in Bacillus thuringiensis and Escherichia coli

The nucleotide sequence of a 1408 base-pair DNA fragment encoding the insecticidal 27,340 Mr delta-endotoxin of Bacillus thuringiensis var. israelensis has been determined by analysis of a recombinant plasmid from Escherichia coli. The hydropathy plot of the protein shows it to be highly hydrophobic, consistent with a postulated cytolytic mechanism of action for the toxin. In addition, the delta-endotoxin transcriptional start points that are used in B. thuringiensis and an E. coli recombinant have been determined. In B. thuringiensis var. israelensis, transcription initiates from a single start point, and gene-specific transcripts are not observed before stage II of sporulation. This is the stage at which delta-endotoxin antigen is first detected, indicating that control of expression is primarily at the transcriptional level for this protein. Analysis of gene-specific transcription in E. coli indicates that at least three start points are utilized in this organism. Interestingly, the highest level of delta-endotoxin mRNA is seen during mid-exponential growth of E. coli and the level appears to decrease as the cells enter the stationary phase of growth.