The multiplication of parvovirus Lu III in a synchronized culture system

Summary

Based on the detection of viral antigen by means of immunofluorescence staining, the replication cycle of parvovirus Lu III was studied in randomly growing and synchronously multiplying HeLa cells. Two different processes could be distinguished in both culture systems. Early events consisted in the appearance of virus specific antigen 3–4 hours following infection independend on the actual physiologic state of the infected cell. The development of intranuclear fluorescence, however, started as early as 8–10 hours p.i. and proved strictly bound to cellular events. Viral replication was finished 16–18 hours p.i. when brightly staining nuclei released distinct fluorescing granules into the cytoplasm or were lost from the cell sheet.

Infection of synchronized HeLa cells at different points of the cell cycle revealed that the shortest possible synchronous replication of Lu III virus could be obtained only if infection occurred about 3 hours after beginning of S phase. Since viral adsorption, penetration, uncoating, as well as transcription of early antigen are independent on cellular physiology and take at least 3 hours, the status of “physiologic competence” necessary for successful completion of virus multiplication may be identical with events in late S phase.

Finally, experiments with UV-inactivated virus suspensions pointed to the presence of a factor which is unaffected by UV irradiation and interferes temporarely with cellular DNA synthesis.