IS1500, AN IS3-LIKE ELEMENT FROM LEPTOSPIRA-INTERROGANS

Copies of an insertion-sequence (IS)-like element were isolated from t wo closely related serovars of Leptospira interrogans sensu stricto, N ucleotide sequence analysis of the 1236 bp element showed a characteri stic IS structure with terminal imperfect inverted repeats (IRs) flank ing a 1159 bp central region, This element was designated IS1500. Four open reading frames (orfA-orfD) were found in the central 'unique' re gion of IS1500, Similarities were detected between ORFA and ORFB and t he putative transposases from members of the IS3 family of transposabl e elements. IS1500 or IS1500-like sequences were also detected in all other pathogenic leptospiral serovars, but not in the saprophytic spec ies L. biflexa. Differences in IS1500 copy numbers in members of the s ame species suggest that this element can transpose. Physical mapping of IS1500 insertions in L. interrogans serovars icterohaemorrhagiae an d pomona showed insertions were only on the large chromosomal replicon , The location of some IS1500 insertions coincides with regions of the genome that have undergone large rearrangements.