Figure 2

Comparisons of structurally aligned nuclease(-like) domains in λ-exonuclease, RecB and RecC. The comparison in a)-c) shows how a single helix in λ-exonuclease (PDB code 1avq; [5]) (a) has been replaced by superimposable α-helical bundles in RecB (b) and RecC (c) (PDB code 1w36; [18]), indicating a more recent shared ancestor of the latter pair. The regions in question are shown as light grey. The remainders of the molecules are coloured in a spectrum from blue (N-terminus) to red (C-terminus). In a) and b), two acidic, metal-ligating residues drawn as sticks mark respective catalytic sites. RecB and RecC are compared in more detail in d) and e), respectively, again coloured from blue to red with the exception of labelled key regions 1 (black), 2 (dark grey) and 3 (grey). Bound metal is shown in b) and d) as spheres while e) additionally shows DNA (shades of pink) and the domain 4 of RecC, coloured uniformly lime green with its pin structure labelled. The DNA strand that penetrates the hoop provided by RecC is shown as a broader cartoon. The RecC "hoop" region (see text for details) is labelled in c) and e) and DNA strand termini are labelled in e).