Multiplication of parvovirus LuIII in a synchronized culture system. IV. Association of viral structural polypeptides with the host cell chromatin

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Abstract
Newly synthesized structural polypeptides of parvovirus LuIII, VP1 (62,000 daltons) and VP2 (74,000 daltons), were detected in nuclei of synchronized, infected HeLa cells at 11-12 h postinfection, i.e., after cells passed through the S phase of the cell cycle. At this time, most of intranuclear viral polypeptides were associated with the chromatin acidic proteins. However, 13-14 h postinfection, about 1/3 of intranuclear VP1 and VP2 also could be extracted in the fraction containing nuclear sap proteins. According to pulse-chase experiments, VP1 and VP2 accumulated in the chromatin with a time lag of 20-30 min. About 90% of these chromatin-associated viral polypeptides represented empty viral capsids. Chromatin prepared at 14 h postinfection contained 90-95% of the total intranuclear viral 16S replicative-form DNA. Since viral replicative-form DNA and empty viral capsids seem to be associated specifically with cellular chromatin, this subnuclear structure may be the site of the synthesis of progeny viral DNA and the formation of complete virions.