Restriction map of the 125-kilobase plasmid of Bacillus thuringiensis subsp. israelensis carrying the genes that encode delta-endotoxins active against mosquito larvae

Abstract

A large plasmid containing all delta-endotoxin genes was isolated from Bacillus thuringiensis subsp. israelensis; restricted by BamHI, EcoRI, HindIII, KpnI, PstI, SacI, and SalI; and cloned as appropriate libraries in Escherichia coli. The libraries were screened for inserts containing recognition sites for BamHI, SacI, and SalI. Each was labeled with 32P and hybridized to Southern blots of gels with fragments generated by cleaving the plasmid with several restriction endonucleases, to align at least two fragments of the relevant enzymes. All nine BamHI fragments and all eight SacI fragments were mapped in two overlapping linkage groups (with total sizes of about 76 and 56 kb, respectively). The homology observed between some fragments is apparently a consequence of the presence of transposons and repeated insertion sequences. Four delta-endotoxin genes (cryIVB-D and cytA) and two genes for regulatory polypeptides (of 19 and 20 kDa) were localized on a 21-kb stretch of the plasmid; without cytA, they are placed on a single BamHI fragment. This convergence enables subcloning of delta-endotoxin genes (excluding cryIVA, localized on the other linkage group) as an intact natural fragment.