[Structural and functional organization of the transposon Tn2555 carrying saccharose utilization genes].

Transposon Tn2555 was isolated from a clinical E. coli strain carries the genes for sucrose utilization. Previously it was shown that Tn2555 is very unstable and undergoes structural rearrangements with a high frequency. Several deletion derivatives of Tn2555 and one with an inversion of the internal segment were found. They form the Tn2555 transposon family. This paper describes further structural and functional analysis of Tn2555. In the course of the experiments on pBR325 (Mob-) mobilization by conjugative RP4 derivatives, containing Tn2555 family elements, it was found, that all of them induce cointegrate formation. Some of these cointegrates were able to dissociate in rec+ and recA E. coli cells. Restriction endonuclease analysis of the resulting plasmids have shown, that among them were the end products of the Tn2555 transposition from RP4 to pBR325. Besides, the pBR325 derivatives, containing a discrete DNA segment of approximately 800 b.p., originating from Tn2555, were found. The segment can transpose from pBR325 to RP4 indicating that it is an insertion sequence. This new IS-element was designated IS286. The size and the genetic properties of IS286 resemble those of the IS1 element. However restriction analysis and Southern hybridization data show no significant homology between IS286 and IS1. It was found that the Tn2555 family elements are flanked by directly repeated IS286. One of them (Tn2555.3) contains an additional copy of IS286 in its internal region.