Thymidine phosphate pools and DNA synthesis after polyoma infection of mouse embryo cells.

We investigated conditions for the incorporation of thymidine-3H into pools of thymidine compounds and into DNA in mouse embryo cells in culture with the purpose of measuring changes in pool sizes and their possible correlation to the rate of DNA synthesis. Thin and dense cultures of embryo cells were grown in Petri dishes during six days. Thymidine triphosphate was the dominating thymidine compound at all time points, while little of the monophosphate was found. After six days thymidine incorporation into DNA had decreased markedly, in contrast to the total pool of thymidine compounds, which was essentially unaltered. In such cultures a relative increase of the diphosphate and the nucleoside occurred. Exposure of stationary mouse embryo cultures to polyoma virus resulted in a marked increase of both DNA synthesis and of total pool size of thymidine compounds. Within this pool the main effect was on thymidine triphosphate. Polyoma infection also gave rise to an increased activity of the enzyme ribonucleotide reductase which provides the deoxyribonudeotides required for DNA synthesis. When proliferating mouse embryo cells were exposed to polyoma virus, we observed only limited effects on DNA synthesis and the pool size of thymidine compounds. This contrasts to the finding with stationary cells.