Unrooted phylogenetic tree of B-family DNA polymerases. The tree was constructed using the conserved blocks from the Exo-Pol alignment (see Additional File 1). The tree is rendered as a scheme, with only the major groups denoted; for the complete tree, with all species indicated, and trees constructed with alternative methods, see Additional File 2. The tree is overlaid with schematics of domain architectures which are given for representatives of each group (Saccharomyces cerevisiae sequences for polymerases α, ζ, δ, ε and those from Sulfolobus solfataricus, Pyrococcus furiosus (pdb:2JGU), and Escherichia coli (pdb:1Q8I) for archaeal minor, archaeal major and proteobacterial groups, respectively). The domains are shown roughly to scale. Inactivated C-terminal domains of polymerases ε are crossed. Dashed line indicates the portion of the sequences corresponding the adjacent tree branch. Zn-finger 2* denotes the distinct version of this module in Pole that is highly similar to the Zn-finger of archaeal PolD (see text for details). The proposed position of the root is shown by an arrow.