Induction of DNA polymerase in Tetrahymena pyriformis

A number of different treatments will induce DNA polymerase in Tetrahymena pyriformis. In the present paper we have studied the induction of DNA polymerase by the inhibitor of DNA synthesis methotrexate plus uridine (M+U) and UV irradiation (after incorporation of bromodeoxyuridine (BUdR) into DNA) in synchronized Tetrahymena populations. We have found that M+U must be present in the nuclear S-period in order to induce the polymerase, and that a dose of UV irradiation which is too low to induce DNA polymerase will do so if the damaging effect of the irradiation is enhanced by incorporation of BUdR into DNA.