FIG. 7.

IS3 family. (A) General organization of IS3 family members. The solid boxes indicate the left (IRL) and right (IRR) terminal IRs. Transcription probably occurs from a weak promoter located partially in IRL. The two consecutive overlapping open reading frames are indicated (orfA and orfB) and are arranged in reading phases 0 and −1 respectively. The products of these frames are shown below. OrfA and OrfB are shown as hatched and open boxes, respectively. The position of a potential helix-turn-helix motif (HTH) is shown as a stippled box in OrfA, and the DDE catalytic domain is shown as a stippled box in OrfB. A potential leucine zipper (LZ) at the C-terminal end of OrfA and extending into OrfAB is also indicated. Each leucine heptad is indicated by an oval. Those present in the OrfA domain are cross-hatched, whereas that deriving from the frameshifted product is open. (B) Dendrogram based on the alignment of the amino acid sequences of predicted OrfA proteins from 40 different elements (left) and 44 predicted OrfB frames (right). The major groups are indicated by brackets. (C) Nucleotide sequences of the terminal IRs of two representative elements of each subgroup, together with some of the elements which do not clearly form part of these groups.