Cloning and nucleotide sequence of a new insertion sequence, IS231N, from a non-serotypable strain of Bacillus thuringiensis

A new IS231 variant, IS231N, has been isolated from an autoagglutinable, no n-serotypable strain of B. thuringiensis. IS231N is 1654 bp in length and i s delimited by two incomplete 20-bp inverted repeats (IRL and IRR) with two mismatches. No direct repeats (DRs were found at the right and left border s of IS231N. Surprisingly, IS231N contains three open reading frames (ORFs) that could code for polypeptides of 329 (ORF1), 118 (ORF2), and 17 (ORF3) amino acids, respectively. IS231N lacks the 5th conserved amino acid domain , called C2, owing to the addition of an adenine residue at nucleotide 1319 . IS231N shows the highest nucleotide identity (99%) with IS231M, another i nsertion sequence previously isolated from the same bacterial strain. IS231 N, however, shares only 83% amino acid identity with IS231M because of nucl eotide substitutions and additions. The ORF1 of IS231N has five fewer amino acids than ORF1 of IS231M. Furthermore, the ORF2-3 putative fusion product in IS231N contains eight fewer amino acids than ORF2 in IS231M. The dendro gram showing the evolutionary relationship between members of the IS231 fam ily and IS231N indicates that IS231N is phylogenetically more closely relat ed to IS231M (83%), followed by IS231F(74%), and is more distant from IS231 V and W(46%).