Fig. 2

Tn5253 attB integration sites in the orthologous rbgA genes of other bacterial species. Genome sequence analysis identified Tn5253 attB sites in the orthologous rbgA genes of 18 other bacterial species with a size ranging between 33 nucleotides of S. gordonii to 84 nucleotides of Streptococcus mitis. The 17-bp E. faecalis attB was at first experimentally found by PCR and sequencing the Tn5253-chromosomal junction fragments of our E. faecalis transconjugants. Then the 17 nucleotides were used as probes for database interrogation. Inside the same bacterial species, different strains can harbour different allelic variants (up to 7 in S. equi). The sequence of the most represented allelic variant was used for the sequence alignment and its frequency is reported. The S. pneumoniae D39 attB variant 1 was used as reference. Tn5253 chromosomal integration, in the original S. pneumoniae host, as in the other functionally characterized streptococcal and enterococcal hosts (shaded), occurs always downstream of a 11-bp conserved sequence, namely the last 11 nucleotides of attB sites. These 11 nucleotides (boxed in blue) are conserved also among the attB sites of other bacterial species. Within the sequences, identical nucleotides are indicated by periods, substitutions are in red. For better alignment, dashes are inserted. The 20 nucleotides belonging to the rbgA coding sequence are underlined