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

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.