Identification and activity of two insertion sequence elements in Rhodococcus sp. strain IGTS8.

Two putative insertion sequence (IS) elements, IS1166 and IS1295, were identified on a plasmid present in Rhodococcus sp. IGTS8. Four copies of IS1166 were present in strain IGTS8: one copy on each of two separate plasmids and two copies on a third plasmid or in the chromosome. Of eight rhodococci tested, only R. zopfii contained a copy of an IS1166-like element. Two mutants of strain IGTS8 were isolated in which an additional copy of IS1166 was present, suggesting that at least one copy of this element may be able to transpose. IS1166 and IS1295 are new members of a family of IS elements which includes IS6120 from Mycobacterium smegmatis, IST2 from Thiobacillus ferrooxidans, IS256 from Staphylococcus aureus and ISRm3 from Rhizobium meliloti. The 24-25-bp inverted repeats of these six elements are highly similar and, with the exception of IS1295, their transposases exhibit moderate identities. In particular, the predicted amino-acid sequence of the transposase from IS1166 is 86% identical to that from the known transposable element IS6120.