Abstract
The activity of RNA polymerase has been determined in the nuclear fraction of normal mouse ovaries, 60-day-old preneoplastic intrasplenic ovarian grafts, and ovarian tumours developed after 7 months of ovary grafting into the spleen. In preneoplastic grafts, RNA polymerase activity corresponds to that of normal ovaries, while in ovarian tumours, the enzyme value was 2-3 times higher. Oestradiol injected for 10 days, acting as depressant of the host pituitary gonadotrophic potency, decreased the enzyme level in the grafts, whereas no change was observed in similarly treated tumours. These facts indicate that hormonal mechanisms regulating the genetic nuclear expression are operating only in the 2-month-old preneoplastic ovarian cell, while autonomy from these regulating mechanisms is achieved by 7-month-old tumour cells.