Effect of salts and other agents on foot-and-mouth disease virus poly (U) polymerase activity

The activity of the purified poly(U) polymerase replication complex of foot-and-mouth disease virus was optimized when 100 mM NH4+ and either 0.75 mM Al3+ or 1.0 mM Fe3+ was added to the standard assay reaction mixture. Zn2+ at concentrations of 10(-5) mM to 5 mM inhibited enzyme activity although all polymerases examined to date have contained zinc. Mercaptoethanol and dithiothreitol inhibited polymerase activity despite the presence of cysteine residues in the viral induced polypeptide of the replication complex, possibly because of their action as metal chelators rather than as reducing agents.