The same orf14 premature stop codon is present in the Tn5253-like element (GenBank FM201786). The element of strain ATCC 700669 (GenBank FM211187) has a deletion of 1 nt in the int coding sequence that determines a frameshift. Completely sequenced Tn916/Tn5251-like elements are also present in many other bacterial species including Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus parauberis, Streptococcus suis, Streptococcus cristatus, check details Streptococcus intermedius, E. faecalis and Ureaplasma urealyticum.

Noteworthy, as found in S. pneumoniae, many of these elements are inserted into other chromosomal genetic elements, such as the 89 K pathogenicity island present in recently sequenced strains of S. suis (Chen et al., 2007). All ORFs, with the exception of orf10, orf20 and orf24, are preceded by a ribosome-binding site. The start codon of orf6 is missing; orf15 starts with the GTG codon and orf20 with TTG. By manual annotation, it was possible to attribute a putative function only to 11 out of 22 ORFs (Table 2). Predicted C59 wnt order gene products were blasted against public protein databases and the Pfam protein family

database, taking into account significant homologies with functionally characterized proteins or good matches with Pfam domains. As reported for Tn916, int and xis are known to be involved in the integration/excision process (Rudy et al., 1997); Int also acts as an accessory protein in the cleavage process that initiates the conjugal transfer mediated by the relaxase Orf20 (Rocco & Churchward, 2006). The tet(M) gene codes for a ribosomal protection protein responsible for tetracycline resistance. orf7 and orf9 code for a putative sigma factor and a putative transcriptional regulator, respectively, and possibly play a role in the gene expression regulation of Tn5251 genes (Celli & Trieu-Cuot, 1998). orf21 is an FtsK-SpoIIIE family protein that may play a role in segregating the replicated element between the donor and the recipient. orf14, coding for a putative cell wall hydrolase, may help degrade the peptidoglycan

during conjugal mating. Orf16 is homologous to TcpF of Clostridium perfringens pCW3, which has been Sitaxentan demonstrated to be essential for the plasmid conjugal transfer. This protein has an ATP-binding motif and is homologous to the VirB4 type IV secretion protein of Gram-negative bacteria that use energy from ATP hydrolysis to pump transposon DNA into the recipient cell (Rabel et al., 2003). orf18 codes for an antirestriction protein that protects the transposon DNA from restriction inhibiting host restriction enzymes (Serfiotis-Mitsa et al., 2008). Tn5251 is inserted into Tn5253, flanked by two different 6-bp-long coupling sequences (CS). Excision of Tn5251 from its attB site produces a CI and a deletion in Tn5253. In the CI, single-stranded overhangs, produced by staggered cleavages of CS, are joined into a heteroduplex (Provvedi et al., 1996).