RADIOAUTOGRAPHY WITH TRITIATED THYMIDINE IN MEASLES AND SENDAI VIRUS-INDUCED CHROMOSOME PULVERIZATIONS

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Abstract
Leukocyte cultures were infected with adenovirus type 12 labeled with tritiated thymidine. Subsequent radioautography has been used to demonstrate that the stage of the cell cycle susceptible to chromosome pulverization by the hemolytic fraction of the measles virus or by intact Sendai virus is the period of DNA synthesis rather than the previously suspected period of prophase and metaphase. Experiments were performed with either the hemolytic fraction of the measles virus or the Sendai virus with a pulse of tritiated thymidine during the last 15 or 30 min. of the experiment and also with a 15-min. pulse of tritiated thymidine early in the experiment before the hemolytic fraction of the measles virus or the Sendai virus was added. In both of these experimental systems when preparations were made and pulverizations localized and the slides dipped in photographic emulsion and exposed for periods of 1 to 2 weeks it was found that silver grains were present over the pulverized chromosomal material and not over the intact metaphase chromosomes indicating that the time of the cell cycle that is susceptible to pulverization by these agents is the DNA synthesis period.