Figure 7.

Proposed scenario for the evolution of the type IIB topoisomerase family. LBCA (last bacterial common ancestor), LACA (last archaeal common ancestor). Dotted double arrows indicate co-evolution of cellular and plasmidic lineages, with subsequent integration or loss of plasmidic topoisomerase VIII-encoding genes in cellular genomes. Black dotted arrow and question mark, possible transfer of a bacterial plasmid to the archaeal domain. For simplicity, both the presence of a few topoisomerase VI enzymes in Bacteria (transferred from Archaea) and the secondary split of the topoisomerase VIII gene in the plasmid PAV109 of Paenibacillus alvei are not indicated.