Figure 8

Secondary structure elements of the IS 2 OrfAB TPase. Elements were generated by the Protein Structure Prediction server [51]. The transposase (TPase) sequence has been color coded to identify the four putative domains; binding (yellow), oligomerization (leucine zipper-like; blue), a middle interval (orange) and the catalytic active site (CAS; green). The numbering of α helix #7 in the middle interval is designed here to reflect the alignment of the six principal α helices found in the IS3 family (Figure 10a). Numbering of α helices 2 and 3 in the CAS reflects the organization of the aligned elements in TPase and integrase sequences of the TPase/retroviral integrase superfamily (Figure 9c). Vertical arrows and substituted amino acids identify the locations of the 23 substitutions within the secondary structures of the IS2 TPase. CAS: catalytic active site; TPase: transposase.