DNA Ligases/biosynthesis; DNA Ligases/genetics; NAD/metabolism; Poxviridae/genetics; Alanine/chemistry; Amino Acid Motifs; Amino Acid Sequence; Aspartic Acid/chemistry; Base Sequence; Catalysis; Cysteine/chemistry; DNA Ligases/isolation & purification; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Evolution, Molecular; Gene Deletion; Genetic Vectors; Models, Biological; Molecular Sequence Data; Mutation; Phylogeny; Protein Binding; Protein Structure, Tertiary; Sequence Homology, Amino Acid; Substrate Specificity; Time Factors; Tyrosine/chemistry; Zinc/metabolism; Zinc Fingers