Factors affecting the release of nuclear ribonucleic acid from the nucleus in vitro.

According to a widely accepted view, the structure of chromosomal deoxyribonucleic acid in the nucleus determines the enzymatic composition of the cytoplasm. An attractive proposition which would explain this genetic control of cytoplasmic enzymes is that deoxyribonucleic acid in some way determines the structure of nuclear ribonucleic acid, that the nuclear ribonucleic acid passes out into the cytoplasm without being degraded, and that this ribonucleic acid controls the synthesis of enzymes and other proteins in the cytoplasm. A possible relation of cytoplasmic ribonucleic acid to proteiri synthesis is now well established, but no relation between deoxyribonucleic acid and nuclear ribonucleic acid, or transfer of nuclear ribonucleic acid to the cytoplasm has been elucidated. One possible proof of transfer of nuclear RNA to the cytoplasm would be to label nuclear RNA in &JO, isolate the nuclei (hereafter referred to as radioactive nuclei), and combine them with a cytoplasmic fraction from a rat which had not been given an injection with radioactive tracer (hereafter referred to as nonradioactive cytoplasm). This reconstituted homogenate could then be incubated in a medium which would permit energy production either by glycolysis or oxidative phosphorylation, and an energy-requiring transfer of RNA from the nucleus to the cytoplasm might be observed in vitro. When such experiments were performed (1, 2) RNA associated with the nuclear fraction was found in the cytoplasmic fraction after incubation. However, the relation between these results in an incubation in vitro, and the physiological phenomena which occur in viva required further investigation. In the present experiments, high concentrations of inhibitors of energy production were examined for their effect on the release of nuclear RNA from radioactive nuclei. These results lead to a study of the effect of ATP, chelating agents, and magnesium concentration on the release. The requirement for an elevated temperature was also investigated. It is demonstrated in these experiments that if there is a physiological “transfer” of RNA from the nucleus to the cytoplasm occurring during the incubation, it does not appear to require energy, it happens in a very short time, and it is prevented by high concentrations of magnesium. These results suggest that chemical or physical factors rather than physiological factors are mainly responsible for the release of nuclear RNA observed in vitro. A requirement for elevated temperatures cannot be satisfactorily explained at present.