Phosphorus Compounds in the Cell Nucleus

1. An investigation has been made of the phosphorus compounds of isolated cell nuclei from fowl erythrocytes, calf thymus, fowl, rabbit and rat liver and the GRCH 15 tumour of the fowl. The results have been expressed both in terms of dry weight of nuclear material and as an absolute amount per single nucleus. 2. Of the total phosphorus present in the cell nucleus 70-90% is present as deoxyribonucleic acid (DNA). 3. The DNA content per nucleus of several samples of nuclei from fowl erythrocytes, and rabbit and rat liver is constant for each nuclear type. This constancy is maintained in rat liver even after a 72 hour fast during which there is a decrease in the RNA, phospholipid and protein content of the nucleus. 4. The nuclei of the GRCH 15 tumour have approximately twice the DNA content (per nucleus) of the nuclei of the normal somatic tissues of the fowl. 5. The observation that DNA phosphorus is metabolically almost inactive has been confirmed in experiments in which was used. 6. The presence of ribonucleic acid (RNA) in the cell nucleus has been established by analytical methods. By means of ionophoresis nuclear RNA has been shown to contain the same four nucleotides as RNA from other sources although the relative amounts of the nucleotides are different from those of cytoplasmic RNA. 7. Nuclear RNA incorporates 32P very rapidly in rat liver and the individual nucleotides show different incorporation rates. 8. The presence of phospholipid in the cell nucleus has been confirmed and its turnover shown to be appreciable. 9. "Phosphoprotein" has been detected in the nucleus in small amount and its phosphorus shown to be metabolically highly active. 10. At least two further protein-bound phosphorus containing compounds have been observed in small amount. Their nature is not yet known