Figure 2.

Superfamilies containing Holliday junction-resolving enzymes. Structural studies of diverse metal ion-dependent nucleases have revealed the existence of two superfamilies. The integrase superfamily, whose founding member is RNaseH, includes viral transposases and integrases as well as the Holliday junction resolving enzymes RuvC, Cce1, and poxviral A22. The nuclease superfamily, with founder member EcoRV, includes all of the type II and probably all of the type I restriction enzymes, as well as diverse DNA repair endo- and exonucleases, the archaeal resolving enzyme Hjc, and T7 endonuclease I. The bacteriophage resolving enzymes RusA and T4 endonuclease VII cannot be assigned to either of these superfamilies at present, although the lineage of the former may be discernible on solution of the crystal structure. The line lengths above bear no relationship to the degree of divergence of family members.