Southern analysis of BT-R 1, the Manduca sexta gene encoding the receptor for the Cry1Ab toxin of Bacillus thuringiensis

Various subspecies of the gram-positive bacterium Bacillus thuringiensis are known to produce a wide array of insecticidal crystal proteins (ICPs) upon sporulation. These ICPs act primarily on the brush border of midgut epithelial cells of susceptible larvae. Recently, a protein of 210?kDa, isolated from the midgut of Manduca sexta, has been demonstrated to bind the Cry1Ab toxin produced by B. thuringiensis subsp. berliner and is therefore postulated to be involved in mediating the toxicity of Cry1Ab. The cDNA encoding the 210?kDa protein, termed BT-R₁ (Bacillus thuringiensis receptor-1), was recently cloned, and shows limited homology to the cadherin superfamily of proteins. Quite naturally, there is a great deal of interest in the characterization of BT-R ₁ , the gene encoding the 210?kDa Cry1Ab binding protein. The studies presented here involve the use of various restriction fragments prepared from the cDNA encoding BT-R₁ as probes of Southern blots bearing M. sexta genomic DNA cleaved with a variety of restriction endonucleases. These Southern blot data reveal that there are two discrete regions within the M. sexta genome which encode sequences homologous to BT-R₁. On the basis of the signal intensities seen on Southern blots, it appears that only one of these genes encodes BT-R₁, whereas the other is a closely related homologue.     

The biotechnology of Bacillus thuringiensis

One of the challenges in the application of biotechnology to pest control is the identification of agents found in nature which can be used effectively. Biotechnology offers the potential of developing pesticides based on such agents which will provide environmentally sound and economically feasible insect control alternatives. Such an agent, the insect pathogen Bacillus thuringiensis, is the subject of intense investigations in several laboratories. Insecticides which use the entomocidal properties of B. thuringiensis are currently produced and sold worldwide; new products are currently in the development stage. Herein, the biology and genetics of B. thuringiensis and the problems associated with current products are critically reviewed with respect to biotechnology. Moreover, the economic and regulatory implications of technologically advanced products are evaluated.