FIG. 4.

Mx8 integrase has four domains of similarity with other integrases. Regions of the predicted product of the Mx8 int gene that are similar to other phage and plasmid integrases are shown. Identical amino acids are indicated in boldface and underlined; similar residues are underlined. Numbers refer to the positions of residues within each Int protein from phages φ42 (11), D29/FRAT1 (44, 16), φ11 (48), and λ (19) and plasmid pSE211 (6). These include an N-terminal basic motif (A), a central domain (B), and two C-terminal domains (C and D) that are conserved among the family of lambdoid integrases and aligned as described elsewhere (2). A tyrosine residue within domain D (arrow) is strictly conserved among the lambdoid integrases; it is the active-site residue that forms an ester linkage with substrate DNAs (33).