Methods for Analysis of Poxvirus DNA Replication

Cytoplasmic replication of poxviruses dictates the encoding of most, if not all, of the trans -acting factors required for faithful genome duplication. Several of these proteins have been identified through genetic and biochemical evaluation, including the catalytic DNA polymerase (E9), an essential and stoichiometric component of the processive polymerase (A20), a singlestrand DNA-binding protein (I3), a type I topoisomerase (H6), the uracil DNA glycosylase (D4), a nucleic acid-independent nucleoside triphosphatase (D5), a serine/threonine protein kinase (B1), and a Holliday Junction resolvase (A22). All of these factors work in concert to faithfully duplicate the viral genome. Although a replication origin has not been defined for the poxviruses, cis -acting sequences found within the telomeric 200 bp have been implicated as necessary and sufficient for minichromosome replication. Replication occurs within cytoplasmic foci from approx 3 to 12 h postinfection. This chapter includes several methodologies to assay and quantitate replication in vivo, visualize replication foci microscopically, and test the integrity of central replication enzymes in vitro.