A transposon-like structure related to the delta-endotoxin gene of Bacillus thuringiensis.

Open Access
Publisher Website
Google Scholar
Abstract
A DNA segment (Th‐sequence) has been found in several strains of Bacillus thuringiensis. This Th‐sequence [3 megadaltons (Md)] induces adjacent deletions when it is located in the pAM beta 1 plasmid derived from Streptococcus faecalis. Electron microscopic examination of reannealed single strands of one plasmid (pMT9) carrying such a deletion revealed that the Th‐sequence corresponds to a single‐stranded loop (2.8 Md) bounded by a short double‐stranded stem (less than 0.2 Md). Southern blotting experiments established that in B. thuringiensis the Th‐sequence was generally located on the large plasmid which also harbours the gene coding for the delta‐endotoxin (crystal protein). Hybridization and heteroduplex analysis of the extrachromosomal DNA from the berliner 1715 strain demonstrated that the crystal gene and the Th‐sequence are located in close vicinity on a 42‐Md plasmid and that they are separated by a 1.3‐Md DNA segment. This DNA segment is repeated in inverted orientation, once immediately adjacent to the Th‐sequence and once 1.8 Md beyond the crystal gene. A model for the organization of these DNA sequences inside a transposon‐like structure is proposed.