IS231V and W from Bacillus thuringiensis subsp. israelensis, two distant members of the IS231 family of insertion sequences.

IS231 constitutes a family of related insertion sequences (IS) from Bacillus thuringiensis. Two new IS231-related elements, IS231V and IS231W, have been isolated from the 72-MDa plasmid of B. thuringiensis subsp. israelensis. These closely related 1964-bp IS are delimited by 22-bp imperfect inverted repeats strongly similar to those of the other iso-IS231. Although the other known IS231 harbor a single long open reading frame (ORF), IS231V and W display two slightly overlapping ORF on the same DNA strand. They show about 50% identity with the transposase of the other iso-IS231. A frameshifting model is proposed for the synthesis of a fusion product which would constitute their active transposase.