The Effect of Streptococcus pneumoniae Infection on RNA Synthesis by Isolated Rat Liver Nuclei

Abstract

Hepatic nuclei were isolated, purified and partially characterized from control and Streptococcus pneumoniae-infected rats. Biochemical and morphological examination showed little contamination by other cell components. Nuclei isolated from the livers of infected rats bound slightly (23%) but not significantly more insulin and showed a marked increase in binding site number when compared to nuclei isolated from control rats. An in vitro system for the incorporation of 1-¹⁴c-uridine-5'-triphosphate (¹⁴c-UTP) into ribonucleic acid (RNA) was developed and characterized. In the presence of hepatic cytosol prepared from either control or infected rats, nuclei isolated from infected rats incorporated significantly more ¹⁴C-UTP into RNA than nuclei isolated from control rats. Similar results were obtained when insulin was substituted for cytosol and the effect was eliminated when cytosol was treated with anit-insulin antibodies. These results suggest that the cytoplasmic factor stimulating incorporation of label into RNA was insulin. These studies suggest that nuclei isolated from infected rats can be stimulated by insulin to synthesize RNA, and that this stimulation may result from an increased number of insulin binding sites on these nuclei.