| dc.description.abstract | Extensive homology between the tet determinant and the flanking regions among most of the streptococcal conjugative transposons suggested that this novel class of mobile elements could have arisen by the 1nsertion of heterologous elements into a basic tet unit, as represented by the smallest known conjugative transposon, Tn916. However, the homology between Tn916 and the 65 kb Tn5253 was limited only to the tet reg1on and did not extend to any other region. Moreover, an 18 kb segment carry1ng the tet determinant that is totally internal to Tn5253 was found to be an independent conjugative transposon, Tn5251. We sought to determine the role of the sequences beyond Tn5251 w1thin Tn5253 in transposition. To this aim, the segment of DNA containing Tn5251 was deleted from within Tn5253 and the deletion mutant strain was used in filter-matings to determine whether the altered element retained 1ts transposit1on properties. The sequences beyond Tn5251 within Tn5253, designated Tn5252, transferred by filter-mat1ng to Streptococcus pneumoniae and Enterococcus faecalis recipient cells at a frequency comparable to that of the parental element. Differences in the structural and functional properties between Tn5251 and Tn5252 seemed to suggest that these belonged to two distinct classes of mobile elements. Moreover, Tn5253, originally detected in a clinical 1solate of ~- pneumoniae, is indeed a compos1te element comprised of two independent conjugative transposons, Tn5252 and Tn5251. These results can be extrapolated to the conclusion that the prototype for this type of element is perhaps a Tn5252-like transposon and not the tet carrying Tn916-like element. | |
