Electron microscopic localization of acridine orange chromatin interaction products in cells transformed by herpes simplex virus type 2.

The purpose of this study was to examine the distribution pattern of acridine orange (AO) binding to DNA in transformed cells and derived tumor cells. Two cell clones from hamster embryonic fibroblasts (HEF) transformed by herpes simplex virus type 2, tumor cells derived from the transformed cell clones, and normal HEF in culture were processed for ultracytochemistry. Uptake studies and autoradiography using [3H] thymidine and [3H]-uridine were also performed. Ultrastructural examination revealed that AO became bound to DNA exclusively within the euchromatin portion of the cell nucleus. The percentages of AO-positive cell nuclei were 18.0% and 15.5% in transformed cell clones and 21.3% and 18.3% in the derived tumor cells, but only 2. 7% in the HEF. The average amounts of AO-chromatin interaction products increased in the transformed and tumor cells. Labeling indices of [3H] thymidine were 28.9% and 33.2% in both the transformed cell clones, 32.4% and 36.9% in their tumor cells, and 3.7% in the HEF. Euchromatin/heterochromatin (EU/HEF) ratios were found to be higher in AO-positive nuclei than in AO-negative nuclei in each cell line. The increase in the number of AO-positive nuclei and in the EU/HET ratios may represent a basic reaction of cell nuclei in transformation and tumorigenesis.