Synthesis of lipids in isolated nuclei from rat thymus and liver cells.

Synthesis of lipids was studied in isolated nuclei from rat thymus and liver cells. On incubation of the isolated nuclei with [2-14C]acetate and [1-14C]glycerol, the label was intensively incorporated into phospholipids and with a significantly lower intensity into fatty acids and cholesterol. Only trace amounts of radioactivity were detected in the lipids of chromatin prepared from isolated thymus nuclei after their incubation, and this suggested that lipids were mainly synthesized on the nuclear membrane. On the preincubation of thymus tissue homogenate with [2-14C]acetate and the subsequent isolation of the nuclei and chromatin, the radioactivity of chromatin lipids was comparable to the radioactivity of nuclear lipids. The findings suggested that in the isolated nuclei the newly synthesized lipids were not transported into chromatin from the nuclear membrane. The specific radioactivities of individual phospholipids and fatty acids were different in the isolated nuclei and in nuclei obtained from preincubated homogenate. Mechanisms of lipid synthesis in isolated nuclei and causes of the different radioactivities of lipids in the isolated nuclei and in the nuclei obtained from the preincubated homogenate are discussed.