Deoxyribonucleic acid (
DNA) synthesis was studied in poxvirus-infected cells by measuring (14)C-thymidine incorporation into viral and host cell
DNA. A complete separation of the two species of
DNA was achieved by combining the previously used "Dounce method" with a separation method based on different reannealing properties of viral and vertebrate
DNA. Shortly after
infection of HeLa cells with poxviruses, a burst of
viral DNA synthesis occurred in the cytoplasm, but a rapid inhibition of host-cell
DNA synthesis in the nucleus was observed. This inhibition of cellular
DNA synthesis was also found if an accumulation of
viral DNA was prevented. At high multiplicites, ultraviolet-irradiated virus inhibited host-cell
DNA synthesis to the same extent as fully infectious poxvirus. Under the same conditions, heating at 60 C for 15 min caused a decrease in the ability of cowpox virus to inhibit host-cell
DNA synthesis, but did not produce the same effect on vaccinia virus strain WR.