INSERTION-SEQUENCE IS1137, A NEW IS3 FAMILY ELEMENT FROM MYCOBACTERIUM-SMEGMATIS

A new insertion sequence (IS) has been isolated from Mycobacterium sme gmatis. It is 1361 bp long and possesses characteristics of the 153 fa mily elements. It harbours 32 bp imperfect inverted repeats at its ext remities and a 3 bp direct repeat flanks the element, possibly as the result of a transposition event. This IS, IS1137, contains three major ORFs. Two of them, ORF A and ORF B show homologies both at the amino acid sequence level and at the organization level with the ORFs encodi ng the transposase of the 153 family elements. IS1137 has a narrow hos t range and was found only in M. smegmatis and M. chitae. The fact tha t IS1137 is not present in the IM. tuberculosis complex strains makes this element a new candidate for transposon mutagenesis in mycobacteri a.