Influence of phosphatidylserine on endogeneous RNA synthesis in isolated rat liver nuclei

The possible involvement of anionic phospholipids in the transcriptional process was studied in isolated rat liver nuclei synthesizing RNA in the presence of phosphatidylserine, which was employed in the form of multillamellar liposomes as a means of delivering the lipid to the nuclei in aqueous medium. The divalent ion requirement for RNA synthesis and the properties of the incubation mixture were not significantly modified by the phospholipid, which increased the rate and the extent of the incorporation of 3H-UMP without changing the endogeneous degradation pattern of the product or affecting the activity of a particular RNA polymerase, as indicated by the sensitivity to amanitin. The thin layer chromatography analysis of the alkaline hydrolysates of the RNA showed that the stimulation involved an increase of the total polyribonucleotide elongation rate. The size of the product was essentially unchanged in the presence of phosphatidylserine, as demonstrated by the qualitative overlapping of the sedimentation profiles of control and lipid treated samples in formamide-sucrose gradients. The release of the H1 fraction from intact nuclei occurring with phosphatidylserine indicated that the DNA template availability was increased by a partial removal of the restrictions imposed by histones, as suggested also by the comparison with heparin and Sarkosyl. These evidences, together with the data accumulated on the occurrence of lipids in chromatin and nuclear matrix, and on their changes related to cell growth, differentiation and malignant transformation, allow a better definition of the role that phospholipids might play in regulating the DNA template availability in the cell.