An investigation of factors affecting poxvirus genetic stability
Vaccinia DNA polymerase consists of both a 5'-3 ' polymerase and 3'-5' , (proofreading) exonuclease activities. The dNTP concentrations affect the exonuclease activity during viral DNA replication and recombination. The strand processing ability of the exonuclease was measured at varying amounts of dNTPs ranging within the putative physiological values. The exonuclease's ability to catalyze duplex strand joining reactions in the presence of dNTPs was also measured. There did not appear to be a significant decrease in activity at physiological dNTP concentrations, however the activity was inhibited at amounts above the physiological range. Leporipoxviruses also encode a DNA repair enzyme, photolyase (M/S127L), which can repair ultraviolet light induced lesions following exposure to photoreactivating light, enhancing virus survival. A myxoma virus was generated containing a deletion of this gene, thus demonstrating that the M/S127L open reading frame did indeed encode a functional photolyase enzyme. The knockout virus was unable to repair UV induced lesions.