A Tn916-like element integrated into the conjugative transposon Tn5253

Tn5253 (formerly _O_(cat-teL)6001) is a conjugative transposon originally found into the chromosome of Streptococcus pneumoniae (6). It is 65.5 kb in size, and carries a cat and a tetM gene (7,8). Tn5253 can be transferred by conjugation to the chromosomes of different streptococcal species: S. pneumoniae, Streptococcus gordonii ( Streptococcus sanguis), Streptococcus pyogenes, Streptococcus agalactiae, and Enterococcus faecal is ( 3, 6). Both genes for drug resistance appeared to be within Lwo separate genetic elements integrated into Tn5253. The cat element was 7.7 kb in size and was flanked by direct repeats ( S. Priebe, unpublished results), whereas the tet element was highly homologous to the 16.4-kb streptococcal conjugative transposon Tn916 (2). Restriction mapping and Southern blot analysis showed that all 5 internal HincII fragments of Tn916 (5) were also p:;:-e::;ent in Tn5253 (Figure 1), and that their size and relative position were similar in the two conjugative transposons. DNA sequence homology was also detected between corresponding HincII fragments. It appeared as if one copy of Tn916, carrying thEi tetM gene was integrated into Tn5253.