Chromosome pulverization in human binucleate cells following colcemid treatment

Under the influence of Colcemid, a substantial number of binucleate human cells from a line infected with herpes-like virus was found to possess pulverized chromosomes. Although this abnormality was also detected in untreated binucleate cells, the increase in the number of pulverized cells after the addition of Colcemid was too striking to be explained by accumulation of spontaneously occurring cells in response to the mitotic inhibition by Colcemid. Furthermore, the induction of pulverization may be dependent upon Colcemid concentration. These findings imply an involvement of Colcemid in the mechanism of pulverization induction in the system studied. When tritiated thymidine was added to the culture medium simultaneously with Colcemid, the majority of binucleate cells with an intact and a pulverized chromosome set incorporated this isotope into the pulverized set only. This obviously suggests that the nuclei in the binucleate cell are asynchronous in DNA synthesis, and that this asynchrony is intimately related to the induction of the pulverization phenomenon. It seems very probable that the late S phase in the late synthesizing nuclei represents a critical stage at which damage to the chromosomes most readily occurs.

Studies on Japanese B Encephalitis Virus

Characteristics of mouse-adapted and hamster kidney (HK) adapted Japanese B encephalitis virus on chick embryo cell cultures have been studied by the plaque method, and the following results obtained: Plaques produced by mouse virus appeared faster than the plaques produced by HK virus. After 4 days of cultivation, mouse virus plaques were clear and 2 to 3 mm in diameter. In contrast, HK virus plaques were hazy and 1 to 2 mm in diameter.Using mouse and HK viruses, a strict linearity of response between plaque count and virus concentration was obtained over a 16-fold range.Maximal adsorption of mouse virus was obtained by 90 min incubation at 36°C, and that of HK virus by 120 minutes. Particles of mouse virus, unadsorbed at the time of agar overlay, subsequently diffused through the agar and produced plaques. In contrast, unadsorbed HK virus was unable to produce plaques.Using mouse and HK viruses, the titers obtained by plaque assay were as high or higher than the LD50 titers in mice or the TCD50 titers in HK cells.