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

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.

Genetic and Physiological Studies of Bacillus Anthracis Related to Development of An Improved Vaccine

“…Lereclus et al (16) reported a model for the structural organization of Tn4A43 (4.2 kb), a crystal gene (ca. 3.7 kb) and two sets of invertsd repeats, IRI (1.7 kb) and IR2 (2.1 kb), on plasmid pBT42, indigenous to the berliner strain of B. thuringiensis.…”

“…They found that these genetic elements were arranged to form a composite transposon-like element on the plasmid. Tn4430 and the crystal gene were separated by one copy of IRI, and these three elements were flanked on each side by another copy of IRI (16).…”

“…al. (16,17) have shown that Tn44!O promotes deletions in DNA sequences adjacent to its endpoints. It is possible then that TnI4IO or insertion elements related to IR1 are responsible for the spontaneous loss of DNA sequences on this region of pX012.…”

A Bacillus thuringiensis subsp. israelensis gene encoding a 125-kilodalton larvicidal polypeptide is associated with inverted repeat sequences

“…has been extensively studied (19,20,25). In several cases, the crystal gene has been found to be flanked by two sets of inverted repeat (IR) sequences and also to be associated with a transposable element, Tn4430 (24,25).…”

“…The sizes of the loops were estimated as 4.49 ± 0. 37 (23,25). The scale used is half of that used for pRX70.…”