In parallel, protein structures of LigIV homologs (human LigI [PDB code: 1X9N ]; Pascal et al., 2004 ), human LigIII (PDB code: 3L2P ; Cotner-Gohara et al., 2010 ), and three archeal D... A ligases (PDB codes 2HIV [ Pascal et al., 2006 ], 2CFM [ Nishida et al., 2006 ], and 3GDE [ Kim et al., 2009 ]) were downloaded from RSBC PDB ( Berman et al., 2000 ), and were structurally aligned using BATON (D.F. Burke, personal communication).
To gain further insights into the role(s) of these residues, the structure of the entire NTase of LigIV was built using Modeller with the NTase-3 structure of LigIV and the experimentally defined domains from LigI (Protein Data Bank [PDB] code: 1X9N ), LigIII (PDB code: 3L2P ), and archeal DNA ligases (PDB codes: 2HIV , 2CFM , and 3GDE ) as templates ( Figure S5 B).