OCCURRENCE OF 3 DIFFERENT BINDING-SITES FOR BACILLUS-THURINGIENSIS DELTA-ENDOTOXINS IN THE MIDGUT BRUSH-BORDER MEMBRANE OF THE POTATO-TUBERMOTH, PHTHORIMAEA-OPERCULELLA (ZELLER)

The potato tuber moth is susceptible to at least three insecticidal cr ystal proteins (ICPs) from Bacillus thuringiensis: CrylA(b), CrylB, an d CrylC. To design useful combinations of toxin genes either in transg enic plants or in new genetically modified B. thuringiensis strains, i t is necessary to determine the binding characteristics of the differe nt ICPs so as not to combine a pair sharing the same binding site. Thi s has been accomplished using two different techniques: I-125-labeling of the ICPs with further measurement of the radioactivity bound to br ush border membrane vesicles, and microscopic visualization of the bou nd ICPs by enzyme-linked reagents such as antibodies or streptavidin u sing biotinylated ICPs. Our results st-cow that CrylA(b), CrylB, and C rylC bind to different sites in the brush border membrane of midgut ep ithelial cells. Also, the affinity of the binding sites for the ICPs a nd their concentration in brush border membrane vesicles has been dete rmined in a laboratory strain and a storage collected population. No s ignificant differences were found between these two strains. (C) 1994 Wiley-iiss, Inc.