Structures of Homologous Composite Transposons Carrying cbaABC Genes from Europe and North America

Abstract

ABSTRACT IS 1071 is a class II transposable element carrying a tnpA gene related to the transposase genes of the Tn 3 family. Copies of IS 1071 that are conserved with more than 99% nucleotide sequence identity have been found as direct repeats flanking a remarkable variety of catabolic gene sequences worldwide. The sequences of chlorobenzoate catabolic transposons found on pBRC60 (Tn 5271 ) in Niagara Falls, N.Y., and on pCPE3 in Bologna, Italy, show that these transposons were formed from highly homologous IS 1071 and cbaABC components (levels of identity, >99.5 and >99.3%, respectively). Nevertheless, the junction sequences between the IS 1071L and IS 1071R elements and the internal DNA differ by 41 and 927 bp, respectively, suggesting that these transposons were assembled independently on the two plasmids. The formation of the right junction in both transposons truncated an open reading frame for a putative aryl-coenzyme A ligase with sequence similarity to benzoate- and p -hydroxybenzoate-coenzyme A ligases of Rhodopseudomonas palustris.