THE IS4 FAMILY OF INSERTION SEQUENCES - EVIDENCE FOR A CONSERVED TRANSPOSASE MOTIF

The eight IS 231 variants characterized so far (IS 231 A-F, V and W) display similar transposases with an overall 40% identity. Comparison with all the prokaryotic transposable elements sequenced so far revealed that the IS 231 transposases share two conserved regions with those of 35 other insertion sequences of wide origins. These insertion sequences, defining the IS 4 family, have a common bipartite organization of their ends and are divided into two similarity groups. Interestingly, the transposase domains conserved within this family display similarities with the well known integrase domain shared by transposases of the IS 3 and IS 15 families, and integrases of retroelements. This domain is also found in IS 30-related elements and Tn7 TnsB protein. Amino acid residues conserved throughout all these prokaryotic and eukaryotic mobile genetic elements define a major transposase/integrase motif, likely to play an important role in the transposition process.