Abstract
The purpose of the research was to investigate the biological features of human cytomegalovirus replication. At the onset of the project five years ago, the amount of information available concerning this subject was limited. During this time results of some comparable studies have been published and the results presented here confirm and complement such studies and contribute to the understanding of virus-directed events in the infected cell. Evidence for virus replication was obtained from (a) microscopic and macroscopic cytopathology (b) cytopathology using acridine orange (c) immunofluorescence (d) quantitative analysis of protein and nucleic acid synthesis using the pulse labelling procedure and (e) titration of infectivity. Virus replication was inhibited by physical and chemical factors including (a) temperature (b) inhibitors of protein synthesis and (c) inhibitors of nucleic acid synthesis. Each inhibitor was added or removed at selected times and the effects were monitored by one or more of the methods mentioned above. It is concluded from the results that viral transcription and translation were essential for the initiation of cell rounding and the early immunofluorescence. The viral protein or oligopeptide responsible may be rich in particular amino acids, for example arginine. An early consequence of infection was the reduction in host-cell macro-molecular synthesis. Cytomegaly developed after the initial cell rounding provided protein synthesis was not interrupted. At 48 hours the infected cells, termed single cell foci (SCF), were easily enumerated. By 84 hours pi infective virus was detected in the cell-free medium and reached a maximum level about 144 hours pi; the level of infectivity in the cell-free medium was maintained for long periods. The onset of DNA synthesis in cells infected with the Rawles virus was 37 hours pi. Protein synthesis was required to initiate and maintain DNA synthesis and uninterrupted DNA synthesis was required for continual virus production. Virus growth was blocked when an inhibitor of host-cell polymerase type II was added to infected cells at 24 hours pi but this inhibitor had no effect at 48 hours pi or later. Virus production and DNA synthesis were blocked at a temperature of 40°C or higher. Two temperature sensitive events were highlighted: one event was completely blocked and one event was partially blocked and the kinetics of the latter event were affected by small changes in supraoptimal temperature. Both events were required for viral DNA synthesis. However, even when viral DMA synthesis had been allowed to occur, production of infective virus was still prevented by shift-up to supraoptimal temperature.