FIG. 3.

IS1 members. Shown is the phylogeny of the IS1 family and comparison of a representative set of terminal IRs. The top panel shows the general organization of members of this family. Red boxes indicate the terminal IRs. Yellow (or white) boxes within the larger IS box indicate ORFs (see the text). (A) Organization of the “classical” bacterial IS1. pIRL indicates the promoter, which drives Tpase synthesis. This class includes those from the archaeal methanogens. (B) The longer of the two Sulfolobus groups carries more-extensive IRs and N- and C-terminal extensions (white boxes) to the Tpase compared to the classical IS1 and the shorter Sulfolobus class. (C) Shorter Sulfolobus class. IRs are approximately the length of those found in the classical IS1 organization. The various Archaea have been color coded as follows for clarity: Sulfolobales, red; methanogens, blue. Bacteria are indicated in black.