Electron microscopy of adenovirus 12 replication. II. High-resolution autoradiography of infected KB cells labeled with tritiated thymidine.

Incorporation of tritiated thymidine by KB cells infected with oncogenic adenovirus 12 was studied by means of high-resolution electron microscopic autoradiography. After a 1-hr pulse with tritiated thymidine, infected and control cultures were fixed at 8, 16, 24, 30, and 36 hr. Infected cultures showed a higher percentage of labeled cells. During early stages, the frequency of silver grains in the nucleus and in the nucleolus was higher in infected material. From 24 hr on, there was an inhibition of nuclear and nucleolar deoxyribonucleic acid (DNA) synthesis. At late stages, one-third of the label was located over nuclear inclusions, type II and IV, previously shown to be composed of DNA and protein, while a large majority of the remaining grains were located over the nucleoplasm. The possibility is considered, that the early increase in nuclear and nucleolar DNA synthesis produced by adeno 12 replication could in part be due to newly synthesized cellular DNA, as has been reported by others with respect to other oncogenic DNA viruses.